diff --git a/.github/workflows/windows-msys2.yml b/.github/workflows/windows-msys2.yml
index 585ab6b8a..00b0b6fac 100644
--- a/.github/workflows/windows-msys2.yml
+++ b/.github/workflows/windows-msys2.yml
@@ -44,7 +44,7 @@ jobs:
           # this is a "prepare" only step for this workflow only, so build
           # without any optional packages as one-time build speeding up this part
           ../configure --without-db --without-curses --without-xml2 --without-json \
-                       --without-iconv --disable-dependency-tracking
+                       --without-iconv --disable-dependency-tracking CFLAGS=--std=c17
 
       - name: Build GnuCOBOL Source Distribution
         shell: msys2 {0}
@@ -133,7 +133,7 @@ jobs:
           tar -xvf gnucobol*.tar.*  --strip-components=1
           mkdir _build
           cd _build
-          ../configure $CFGOPT
+          PATH="$PATH:/c/Program Files/Git/usr/bin" ../configure $CFGOPT CFLAGS=--std=c17
 
       - name: Build GnuCOBOL
         shell: msys2 {0}
diff --git a/ChangeLog b/ChangeLog
index 30513f9d0..105f37be1 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,4 +1,8 @@
 
+2025-05-13  David Declerck <david.declerck@ocamlpro.com>
+
+	* configure.ac: testing working diff with the option to override by DIFF
+
 2025-03-27  Simon Sobisch <simonsobisch@gnu.org>
 
 	* configure.ac: fix --without-iconv; use iconv includes, if necessary;
diff --git a/configure.ac b/configure.ac
index ee476bbba..de67a0e3f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -620,6 +620,17 @@ AC_PROG_LEX([noyywrap])
 AX_PROG_FLEX
 AX_PROG_BISON
 
+AC_CACHE_CHECK([for diff], [ac_cv_path_DIFF],
+  [AC_PATH_PROGS_FEATURE_CHECK([DIFF], [diff],
+    [[echo "x" > fx1 ; echo "x" > fx2 ; echo "y" > fy
+      "$ac_path_DIFF" fx1 fx2 >/dev/null ; res0=$?
+      "$ac_path_DIFF" fx1 fy >/dev/null ; res1=$?
+      rm -f fx1 fx2 fy
+      test $res0 = 0 -a $res1 = 1 \
+      && ac_cv_path_DIFF="$ac_path_DIFF" ac_path_DIFF_found=:]],
+    [AC_MSG_ERROR([could not find a working diff])])])
+AC_SUBST([DIFF], [$ac_cv_path_DIFF])
+
 AC_ARG_VAR(DIFF_FLAGS, arguments passed to diff)
 AC_MSG_CHECKING([for diff arguments])
 case "$DIFF_FLAGS" in
@@ -627,7 +638,7 @@ case "$DIFF_FLAGS" in
    AC_MSG_RESULT([specified as $DIFF_FLAGS])
   ;;
   *)
-   diff $DIFF_FLAGS --strip-trailing-cr --version 1>/dev/null  2>&1
+   "$DIFF" $DIFF_FLAGS --strip-trailing-cr --version 1>/dev/null  2>&1
    if test $? -eq 0; then
       if test -z "$DIFF_FLAGS"; then
          DIFF_FLAGS="--strip-trailing-cr"
diff --git a/tests/ChangeLog b/tests/ChangeLog
index 936537c3b..f165c3bf2 100644
--- a/tests/ChangeLog
+++ b/tests/ChangeLog
@@ -1,4 +1,10 @@
 
+2025-05-13  David Declerck <david.declerck@ocamlpro.com>
+
+	* atlocal.in, atlocal_win, cobol85/Makefile.am,
+	  cobol85/Makefile.module.in, testsuite.src/*.at:
+	  use the new DIFF variable to invoke the diff command
+
 2025-03-16  Simon Sobisch <simonsobisch@gnu.org>
 
 	* atlocal.in: adjusted to handle newer MSYS2's setting OSTYPE=cygwin
diff --git a/tests/atlocal.in b/tests/atlocal.in
index 0666ba106..4b4cfc355 100644
--- a/tests/atlocal.in
+++ b/tests/atlocal.in
@@ -53,6 +53,13 @@ else
 	ABS_COBCRUN="$(which cobcrun)"
 fi
 
+# We need to define a diff function, because:
+# - we want autotest to use our custom diff command
+# - the DIFF variable might contain spaces
+diff() {
+  command "@DIFF@" @DIFF_FLAGS@ "$@"
+}
+DIFF=diff
 AWK=@AWK@
 GREP=@GREP@
 SED=@SED@
diff --git a/tests/atlocal_win b/tests/atlocal_win
index 227bfffdf..9ea5f98e3 100644
--- a/tests/atlocal_win
+++ b/tests/atlocal_win
@@ -40,6 +40,7 @@ LOCAL_ENV=""
 PATH="${COB_WIN_BUILDPATH}:${PATH}"
 export PATH
 
+DIFF=diff
 AWK=awk
 GREP=grep
 SED=sed
diff --git a/tests/cobol85/Makefile.am b/tests/cobol85/Makefile.am
index edc99d9be..78fb71416 100644
--- a/tests/cobol85/Makefile.am
+++ b/tests/cobol85/Makefile.am
@@ -1,7 +1,7 @@
 #
 # Makefile gnucobol/tests/cobol85
 #
-# Copyright (C) 2002-2012, 2015-2024 Free Software Foundation, Inc.
+# Copyright (C) 2002-2012, 2015-2025 Free Software Foundation, Inc.
 # Written by Keisuke Nishida, Roger While, Simon Sobisch
 #
 # This file is part of GnuCOBOL.
@@ -59,6 +59,7 @@ COBC_FLAGS = -std=cobol85 -debug $(COBOL_FLAGS)
 
 CURL_FLAGS = 
 WGET_FLAGS = -t1 -T5
+DIFF = @DIFF@
 DIFF_FLAGS = @DIFF_FLAGS@
 
 PRE_INST_ENV = "$(abs_top_builddir)/pre-inst-env"
@@ -163,7 +164,7 @@ diff:
 	@echo "Comparing test results for each module"
 	@retd=0; for m in $(MODULES); do \
 		echo "diff $$m/report.txt..."; \
-		diff $(DIFF_FLAGS) "$(srcdir)/$$m.txt" "$$m/report.txt"; \
+		"$(DIFF)" $(DIFF_FLAGS) "$(srcdir)/$$m.txt" "$$m/report.txt"; \
 		ret=$$? && if test $$ret -gt $$retd; then retd=$$ret; fi \
 	done; \
 		if test $$retd -gt 1; then exit $$retd; fi
@@ -175,7 +176,7 @@ diff-summary:
 	$(MAKE) summary.log
 	@echo "Comparing total test results..."
 	@echo "diff $(SUMMARY)..."
-	@diff $(DIFF_FLAGS) "$(srcdir)/$(SUMMARY)" "summary.log"
+	@"$(DIFF)" $(DIFF_FLAGS) "$(srcdir)/$(SUMMARY)" "summary.log"
 	@echo Done
 
 newcob.val.Z:
@@ -246,6 +247,7 @@ $(MODULES_ALL): newcob.val EXEC85$(EXEEXT) $(srcdir)/EXEC85.conf.in Makefile.mod
 	@(export CBL_LIST="`ls $@/*.CBL | cut -f2 -d/ | tr '\n' ' '`" && \
 	 $(SED) -e 's/##MODULE##/'"$@"'/'            \
 	        -e 's|##COB85DIR##|'$(abs_srcdir)'|' \
+	        -e 's|##DIFF##|'"$(DIFF)"'|' \
 	        -e 's|##DIFF_FLAGS##|'"$(DIFF_FLAGS)"'|' \
 	        -e 's|##PERL##|'"$(PERL)"'|' \
 	        -e 's|##TESTS##|'"` echo $$CBL_LIST | $(SED) -e 's/\.CBL//g'`"'|' \
diff --git a/tests/cobol85/Makefile.module.in b/tests/cobol85/Makefile.module.in
index 08193c62e..6eec6b425 100644
--- a/tests/cobol85/Makefile.module.in
+++ b/tests/cobol85/Makefile.module.in
@@ -1,7 +1,7 @@
 #
 # Makefile gnucobol/tests/cobol85/##MODULE##
 #
-# Copyright (C) 2002-2012, 2015-2020, 2022-2023 Free Software Foundation, Inc.
+# Copyright (C) 2002-2012, 2015-2020, 2022-2023, 2025 Free Software Foundation, Inc.
 # Written by Keisuke Nishida, Roger While, Simon Sobisch
 #
 # This file is part of GnuCOBOL.
@@ -23,6 +23,7 @@ TESTS = ##TESTS##
 TESTS_LOCAL = ##TESTS_LOCAL##
 
 RM = rm -rf
+DIFF = ##DIFF##
 DIFF_FLAGS = ##DIFF_FLAGS##
 
 PERL = ##PERL##
@@ -61,7 +62,7 @@ test-local:
 diff: report.txt
 	@echo
 	@echo "Comparing test results for module directory ##MODULE##"
-	@diff $(DIFF_FLAGS) ##COB85DIR##/##MODULE##.txt report.txt || true
+	@"$(DIFF)" $(DIFF_FLAGS) ##COB85DIR##/##MODULE##.txt report.txt || true
 
 test-O:
 	@. ../../atconfig && . ../../atlocal && $(MAKE) $@-local
@@ -93,7 +94,7 @@ $(TESTS):
 $(TESTS_LOCAL): libs-local
 	@echo "Running single test `echo $@ | sed -e 's|-.*||g'`"
 	@$(PERL) ##COB85DIR##/report.pl `echo $@ | sed -e 's|-.*||g'` 2>$@.log
-	@grep `echo $@ | sed -e 's|-.*||g'` ##COB85DIR##/##MODULE##.txt | diff - $@.log
+	@grep `echo $@ | sed -e 's|-.*||g'` ##COB85DIR##/##MODULE##.txt | "$(DIFF)" - $@.log
 	@rm -rf $@.log
 
 clean: clean-log clean-db clean-debug clean-bin
diff --git a/tests/testsuite.src/listings.at b/tests/testsuite.src/listings.at
index 26d90b67e..a43d5daf1 100644
--- a/tests/testsuite.src/listings.at
+++ b/tests/testsuite.src/listings.at
@@ -77,7 +77,7 @@ AT_CHECK([$COMPILE_ONLY -t prog.lst -tlines=2 prog.cob], [0], [],
 ])
 
 AT_CHECK([$UNIFY_LISTING prog.lst prog.lis], [0], [], [])
-AT_CHECK([diff expected.lst prog.lis], [0], [], [])
+AT_CHECK([$DIFF expected.lst prog.lis], [0], [], [])
 
 AT_CLEANUP
 
@@ -1709,9 +1709,9 @@ SIZE  TYPE           LVL  NAME                           PICTURE
 # Check once with $COMPILE and once with $COMPILE_ONLY.
 # This tests whether codegen affects the listing.
 AT_CHECK([$COMPILE $LISTING_FLAGS -t prog.lst -ftsymbols prog.cob], [0], [], [])
-AT_CHECK([diff prog20.lst prog.lst], [0], [], [])
+AT_CHECK([$DIFF prog20.lst prog.lst], [0], [], [])
 AT_CHECK([$COMPILE_LISTING -t prog2.lst -ftsymbols prog.cob], [0], [], [])
-AT_CHECK([diff prog20.lst prog2.lst], [0], [], [])
+AT_CHECK([$DIFF prog20.lst prog2.lst], [0], [], [])
 
 AT_CHECK([rm -f prog.lst prog2.lst], [0], [], [])
 
@@ -1776,9 +1776,9 @@ SIZE  TYPE           LVL  NAME                           PICTURE
 # Check once with $COMPILE and once with $COMPILE_ONLY.
 # This tests whether codegen affects the listing.
 AT_CHECK([$COMPILE $LISTING_FLAGS -t prog.lst -ftsymbols progb.cob], [0], [], [])
-AT_CHECK([diff prog20b.lst prog.lst], [0], [], [])
+AT_CHECK([$DIFF prog20b.lst prog.lst], [0], [], [])
 AT_CHECK([$COMPILE_LISTING -t prog2.lst -ftsymbols progb.cob], [0], [], [])
-AT_CHECK([diff prog20b.lst prog2.lst], [0], [], [])
+AT_CHECK([$DIFF prog20b.lst prog2.lst], [0], [], [])
 
 AT_CHECK([rm -f prog.lst prog2.lst], [0], [], [])
 
@@ -1850,9 +1850,9 @@ progc.cob:13: error: syntax error, unexpected ., expecting DIVISION
 # Check once with $COMPILE and once with $COMPILE_ONLY.
 # This tests whether codegen affects the listing.
 AT_CHECK([$COMPILE $LISTING_FLAGS -t prog.lst -ftsymbols progc.cob], [1], [], [ignore])
-AT_CHECK([diff prog20c.lst prog.lst], [0], [], [])
+AT_CHECK([$DIFF prog20c.lst prog.lst], [0], [], [])
 AT_CHECK([$COMPILE_LISTING -t prog2.lst -ftsymbols progc.cob], [1], [], [ignore])
-AT_CHECK([diff prog20c.lst prog2.lst], [0], [], [])
+AT_CHECK([$DIFF prog20c.lst prog2.lst], [0], [], [])
 
 AT_CLEANUP
 
@@ -2027,10 +2027,10 @@ prog-2.cob:16: warning: unreachable statement 'ACCEPT'
 # This tests whether codegen affects the listing.
 
 AT_CHECK([$COMPILE $LISTING_FLAGS -Wunreachable -t prog.lst -Xref -ftsymbols prog-1.cob prog-2.cob], [0], [], [ignore])
-AT_CHECK([diff expected.lst prog.lst], [0], [], [])
+AT_CHECK([$DIFF expected.lst prog.lst], [0], [], [])
 
 AT_CHECK([$COMPILE_LISTING -Wunreachable -t prog.lst -Xref -ftsymbols prog-1.cob prog-2.cob], [0], [], [ignore])
-AT_CHECK([diff expected.lst prog.lst], [0], [], [])
+AT_CHECK([$DIFF expected.lst prog.lst], [0], [], [])
 
 AT_CLEANUP
 
@@ -2307,12 +2307,12 @@ SIZE  TYPE           LVL  NAME                           PICTURE
 
 ])
 
-AT_CHECK([diff prog15-1.lst prog.lst], [0], [], [])
+AT_CHECK([$DIFF prog15-1.lst prog.lst], [0], [], [])
 
 # verify that the symbol listing is identical if full codegen was done
 AT_CHECK([$COMPILE $LISTING_FLAGS -t prog2.lst -tlines=0 -fno-tsource -fno-tmessages -ftsymbols prog3.cob], [0], [], [])
 
-AT_CHECK([diff prog15-1.lst prog2.lst], [0], [], [])
+AT_CHECK([$DIFF prog15-1.lst prog2.lst], [0], [], [])
 
 AT_CLEANUP
 
@@ -2478,7 +2478,7 @@ SIZE  TYPE           LVL  NAME                           PICTURE
 0 errors in compilation group
 ])
 
-AT_CHECK([diff prog17-32.lst prog.lst], [0], [], [])
+AT_CHECK([$DIFF prog17-32.lst prog.lst], [0], [], [])
 
 ,
 
@@ -2587,7 +2587,7 @@ SIZE  TYPE           LVL  NAME                           PICTURE
 0 errors in compilation group
 ])
 
-AT_CHECK([diff prog17-64.lst prog.lst], [0], [], [])
+AT_CHECK([$DIFF prog17-64.lst prog.lst], [0], [], [])
 
 )
 
@@ -3666,7 +3666,7 @@ prog.cob:81: warning: uncommon parentheses
 50 errors in compilation group
 ])
 
-AT_CHECK([diff expected.lst prog.lst], [0])
+AT_CHECK([$DIFF expected.lst prog.lst], [0])
 
 AT_CLEANUP
 
diff --git a/tests/testsuite.src/run_extensions.at b/tests/testsuite.src/run_extensions.at
index cfa04244e..95e34f256 100644
--- a/tests/testsuite.src/run_extensions.at
+++ b/tests/testsuite.src/run_extensions.at
@@ -1455,7 +1455,7 @@ AT_DATA([reference],
 040310Howdy 1 2 3<>  01***Abcdefghij. 34545656702***Abcdefghij. 45656767803***Abcdefghij. 567678789<>
 ])
 
-AT_CHECK([diff reference SEQODO], [0], [], [])
+AT_CHECK([$DIFF reference SEQODO], [0], [], [])
 
 AT_CLEANUP
 
diff --git a/tests/testsuite.src/run_file.at b/tests/testsuite.src/run_file.at
index 57c4eee86..de6eeff83 100644
--- a/tests/testsuite.src/run_file.at
+++ b/tests/testsuite.src/run_file.at
@@ -854,16 +854,16 @@ AT_CHECK([$COBCRUN_DIRECT ./prog], [0], [], [])
 AT_DATA([reference],
 [hi
 ])
-AT_CHECK([diff reference whatever], [0], [], [])
+AT_CHECK([$DIFF reference whatever], [0], [], [])
 
 AT_CHECK([$COMPILE -fassign-clause=dynamic -fno-implicit-assign-dynamic-var prog.cob], [0], [], [])
 AT_CHECK([$COBCRUN_DIRECT ./prog], [0], [], [])
-AT_CHECK([diff reference whatever], [0], [], [])
+AT_CHECK([$DIFF reference whatever], [0], [], [])
 
 AT_CHECK([$COMPILE -fassign-clause=dynamic prog.cob], [0], [], [])
 AT_CAPTURE_FILE([out.txt])
 AT_CHECK([$COBCRUN_DIRECT ./prog], [0], [], [])
-AT_CHECK([diff reference out.txt], [0], [], [])
+AT_CHECK([$DIFF reference out.txt], [0], [], [])
 
 AT_CLEANUP
 
@@ -4323,7 +4323,7 @@ AT_DATA([prog2.cob], [
 
 AT_CHECK([$COMPILE prog2.cob], [0], [], [])
 AT_CHECK([$COBCRUN_DIRECT ./prog2], [0], [], [])
-AT_CHECK([diff prog.cob prog3.cob], [0], [], [])
+AT_CHECK([$DIFF prog.cob prog3.cob], [0], [], [])
 
 AT_CLEANUP
 
@@ -4779,7 +4779,7 @@ Write 1: STATUS IS 00 LENGTH IS 009
 Write 2: STATUS IS 00 LENGTH IS 064
 ], [])
 
-AT_CHECK([diff reference TEST-FILE], [0], [], [])
+AT_CHECK([$DIFF reference TEST-FILE], [0], [], [])
 
 # same check with dialect option (4.x feature)
 # AT_CHECK([$COMPILE -std=gc31 prog.cob], [0], [], [])
@@ -4798,7 +4798,7 @@ AT_CHECK([diff reference TEST-FILE], [0], [], [])
 # Write 2: STATUS IS 00 LENGTH IS 064
 # ], [])
 #
-# AT_CHECK([diff reference TEST-FILE], [0], [], [])
+# AT_CHECK([$DIFF reference TEST-FILE], [0], [], [])
 
 AT_CLEANUP
 
@@ -4914,7 +4914,7 @@ AT_DATA([reference],
 Record 2................................
 ])
 
-AT_CHECK([diff reference TEST-FILE], [0], [], [])
+AT_CHECK([$DIFF reference TEST-FILE], [0], [], [])
 
 # same check with dialect option (4.x feature)
 # AT_CHECK([$COMPILE -std=gc31 prog.cob], [0], [], [])
@@ -4934,7 +4934,7 @@ AT_CHECK([diff reference TEST-FILE], [0], [], [])
 # Write 2: STATUS IS 00 LENGTH IS 064
 # ], [])
 #
-# AT_CHECK([diff reference TEST-FILE], [0], [], [])
+# AT_CHECK([$DIFF reference TEST-FILE], [0], [], [])
 
 AT_CLEANUP
 
@@ -5221,7 +5221,7 @@ AT_CHECK([$COMPILE prog.cob], [0], [], [])
 AT_CHECK([COB_CURRENT_DATE="2015/02/06 16:40:52" $COBCRUN_DIRECT ./prog], [0],
 [Normal termination, ending status: 10
 ], [])
-AT_CHECK([diff mini-report reference-report], [0], [], [])
+AT_CHECK([$DIFF mini-report reference-report], [0], [], [])
 
 AT_CLEANUP
 
@@ -5511,7 +5511,7 @@ AT_XFAIL_IF([true])
 AT_CHECK([$COBCRUN_DIRECT ./prog], [0],
 [Normal termination, ending status: 10
 ], [])
-AT_CHECK([diff mini-report reference-report], [0], [], [])
+AT_CHECK([$DIFF mini-report reference-report], [0], [], [])
 
 AT_CLEANUP
 
@@ -8882,7 +8882,7 @@ Key: PRE00000 is PRESTIGE OFFICE FURNITURE Disk=8470    .
 Hit End of File after 11
 ])
 
-AT_CHECK([diff reference prog.out], [0], [], [])
+AT_CHECK([$DIFF reference prog.out], [0], [], [])
 
 # verify that all of this works with wrapping to EXTFH calls
 # and that those don't trash the FH--FCD allocated memory
@@ -8890,7 +8890,7 @@ AT_CHECK([diff reference prog.out], [0], [], [])
 AT_CHECK([$COMPILE -fcallfh=EXTFH -o extfh prog.cob], [0], [], [])
 AT_CHECK([$COBCRUN_DIRECT ./extfh 1>prog.out], [0], [], [])
 
-AT_CHECK([diff reference prog.out], [0], [], [])
+AT_CHECK([$DIFF reference prog.out], [0], [], [])
 
 
 AT_CLEANUP
@@ -9484,7 +9484,7 @@ AT_DATA([reference],
  10
 ])
 
-AT_CHECK([diff reference TEST-OUT], [0], [], [])
+AT_CHECK([$DIFF reference TEST-OUT], [0], [], [])
 
 AT_CLEANUP
 
@@ -9677,7 +9677,7 @@ THE LAMB WAS GRAND AND A GRANDMA
 THE OLD EWE CHORTLED
 ])
 
-AT_CHECK([diff reference report.txt], [0])
+AT_CHECK([$DIFF reference report.txt], [0])
 
 AT_CLEANUP
 
@@ -11444,7 +11444,7 @@ AT_DATA([reference],
  10
 ])
 
-AT_CHECK([diff reference TEST-OUT], [0], [], [])
+AT_CHECK([$DIFF reference TEST-OUT], [0], [], [])
 
 AT_CLEANUP
 
@@ -12495,12 +12495,12 @@ Ph=8787458374 Key: OLD00000 is OLD TYME PIZZA MFG. CO.  .
 Hit End of File
 ])
 
-AT_CHECK([diff reference prog.out], [0], [], [])
+AT_CHECK([$DIFF reference prog.out], [0], [], [])
 
 AT_CHECK([$COMPILE -fcallfh=EXTFH -o extfh prog.cob], [0], [], [])
 AT_CHECK([$COBCRUN_DIRECT ./extfh 1>prog.out], [0], [], [])
 
-AT_CHECK([diff reference prog.out], [0], [], [])
+AT_CHECK([$DIFF reference prog.out], [0], [], [])
 
 AT_CLEANUP
 
@@ -12757,7 +12757,7 @@ AT_DATA([prog1.cob], [
 ])
 AT_CHECK([$COMPILE -Wno-unfinished -Wno-others prog1.cob], [0], [], [])
 AT_CHECK([$COBCRUN_DIRECT ./prog1 1>prog1.out], [0], [], [])
-AT_CHECK([diff reference_ascii prog1.out], [0], [], [])
+AT_CHECK([$DIFF reference_ascii prog1.out], [0], [], [])
 
 # Testing ASCII file collating sequence using flag
 AT_DATA([prog2.cob], [
@@ -12767,7 +12767,7 @@ AT_DATA([prog2.cob], [
 ])
 AT_CHECK([$COMPILE -Wno-unfinished -fdefault-file-colseq=ASCII prog2.cob], [0], [], [])
 AT_CHECK([$COBCRUN_DIRECT ./prog2 1>prog2.out], [0], [], [])
-AT_CHECK([diff reference_ascii prog2.out], [0], [], [])
+AT_CHECK([$DIFF reference_ascii prog2.out], [0], [], [])
 
 
 # Testing ASCII file collating sequence + EBCDIC key collating sequence using clauses
@@ -12778,7 +12778,7 @@ AT_DATA([prog3.cob], [
 ])
 AT_CHECK([$COMPILE -Wno-unfinished -Wno-others prog3.cob], [0], [], [])
 AT_CHECK([$COBCRUN_DIRECT ./prog3 1>prog3.out], [0], [], [])
-AT_CHECK([diff reference_ascii_ebcdic prog3.out], [0], [], [])
+AT_CHECK([$DIFF reference_ascii_ebcdic prog3.out], [0], [], [])
 
 # Testing ASCII file collating sequence using flag + EBCDIC key collating sequence using clause
 AT_DATA([prog4.cob], [
@@ -12788,7 +12788,7 @@ AT_DATA([prog4.cob], [
 ])
 AT_CHECK([$COMPILE -Wno-unfinished -fdefault-file-colseq=ASCII prog4.cob], [0], [], [])
 AT_CHECK([$COBCRUN_DIRECT ./prog4 1>prog4.out], [0], [], [])
-AT_CHECK([diff reference_ascii_ebcdic prog4.out], [0], [], [])
+AT_CHECK([$DIFF reference_ascii_ebcdic prog4.out], [0], [], [])
 
 # Testing EBCDIC file collating sequence using clause
 AT_DATA([prog5.cob], [
@@ -12798,7 +12798,7 @@ AT_DATA([prog5.cob], [
 ])
 AT_CHECK([$COMPILE -Wno-unfinished -Wno-others prog5.cob], [0], [], [])
 AT_CHECK([$COBCRUN_DIRECT ./prog5 1>prog5.out], [0], [], [])
-AT_CHECK([diff reference_ebcdic prog5.out], [0], [], [])
+AT_CHECK([$DIFF reference_ebcdic prog5.out], [0], [], [])
 
 # Testing EBCDIC file collating sequence using flag
 AT_DATA([prog6.cob], [
@@ -12808,7 +12808,7 @@ AT_DATA([prog6.cob], [
 ])
 AT_CHECK([$COMPILE -Wno-unfinished -Wno-others -fdefault-file-colseq=EBCDIC prog6.cob], [0], [], [])
 AT_CHECK([$COBCRUN_DIRECT ./prog6 1>prog6.out], [0], [], [])
-AT_CHECK([diff reference_ebcdic prog6.out], [0], [], [])
+AT_CHECK([$DIFF reference_ebcdic prog6.out], [0], [], [])
 
 # Testing EBCDIC file collating sequence + ASCII key collating sequence using clauses
 AT_DATA([prog7.cob], [
@@ -12818,7 +12818,7 @@ AT_DATA([prog7.cob], [
 ])
 AT_CHECK([$COMPILE -Wno-unfinished -Wno-others prog7.cob], [0], [], [])
 AT_CHECK([$COBCRUN_DIRECT ./prog7 1>prog7.out], [0], [], [])
-AT_CHECK([diff reference_ebcdic_ascii prog7.out], [0], [], [])
+AT_CHECK([$DIFF reference_ebcdic_ascii prog7.out], [0], [], [])
 
 # Testing EBCDIC file collating sequence using flag + ASCII key collating sequence using clause
 AT_DATA([prog8.cob], [
@@ -12828,7 +12828,7 @@ AT_DATA([prog8.cob], [
 ])
 AT_CHECK([$COMPILE -Wno-unfinished -Wno-others -fdefault-file-colseq=EBCDIC prog8.cob], [0], [], [])
 AT_CHECK([$COBCRUN_DIRECT ./prog8 1>prog8.out], [0], [], [])
-AT_CHECK([diff reference_ebcdic_ascii prog8.out], [0], [], [])
+AT_CHECK([$DIFF reference_ebcdic_ascii prog8.out], [0], [], [])
 
 AT_CLEANUP
 
@@ -14705,12 +14705,12 @@ DELETE FILES
 AT_CHECK([$COMPILE prog1.cob])
 AT_DATA([file1.txt], [])
 AT_CHECK([$COBCRUN_DIRECT ./prog1 > prog1.txt])
-AT_CHECK([diff expected.txt prog1.txt])
+AT_CHECK([$DIFF expected.txt prog1.txt])
 
 AT_CHECK([$COMPILE prog2.cob])
 AT_DATA([file1.txt], [])
 AT_CHECK([$COBCRUN_DIRECT ./prog2 > prog2.txt])
-AT_CHECK([diff expected.txt prog2.txt])
+AT_CHECK([$DIFF expected.txt prog2.txt])
 
 AT_CLEANUP
 
diff --git a/tests/testsuite.src/run_misc.at b/tests/testsuite.src/run_misc.at
index de99a79fe..69eef9c1f 100644
--- a/tests/testsuite.src/run_misc.at
+++ b/tests/testsuite.src/run_misc.at
@@ -10208,7 +10208,7 @@ Line:    572            CLOSE
 Line:    333            STOP RUN
 ])
 
-AT_CHECK([diff reference trace.txt], [0], [], [])
+AT_CHECK([$DIFF reference trace.txt], [0], [], [])
 
 AT_CHECK([$COMPILE -ftrace prog.cob -o prog_s], [0], [], [])
 
@@ -10348,7 +10348,7 @@ Paragraph: LISTFILE                        -    387
 
 AT_CAPTURE_FILE([trace_append.txt])
 
-AT_CHECK([diff reference_append trace_append.txt], [0], [], [])
+AT_CHECK([$DIFF reference_append trace_append.txt], [0], [], [])
 
 AT_CLEANUP
 
@@ -10897,7 +10897,7 @@ AT_CHECK([$SED -e 's/_$//' reference_tmpl > reference], [0], [], [])
 AT_CHECK([$SED -e 's/compiled ... .. .... ..:..:../compiled MMM DD YYYY HH:MM:SS/g' \
 tstdump.dump > tstdump.sed], [0], [], [])
 
-AT_CHECK([diff reference tstdump.sed], [0], [], [])
+AT_CHECK([$DIFF reference tstdump.sed], [0], [], [])
 
 # recheck with COBC_GEN_DUMP_COMMENTS, which may not change the output
 AT_CHECK([COBC_GEN_DUMP_COMMENTS=1 \
@@ -10917,7 +10917,7 @@ dump written to tstdump.dump
 AT_CHECK([$SED -e 's/compiled ... .. .... ..:..:../compiled MMM DD YYYY HH:MM:SS/g' \
 tstdump.dump > tstdump.sed], [0], [], [])
 
-AT_CHECK([diff reference tstdump.sed], [0], [], [])
+AT_CHECK([$DIFF reference tstdump.sed], [0], [], [])
 
 
 # using both
@@ -10948,7 +10948,7 @@ dump written to tstdump.dump
 AT_CHECK([$SED -e 's/compiled ... .. .... ..:..:../compiled MMM DD YYYY HH:MM:SS/g' \
 tstdump.dump > tstdump.sed], [0], [], [])
 
-AT_CHECK([diff reference tstdump.sed], [0], [], [])
+AT_CHECK([$DIFF reference tstdump.sed], [0], [], [])
 
 
 
@@ -10984,7 +10984,7 @@ X is 000005441
 AT_CHECK([$SED -e 's/Started by .*prog.exe/Started by .\/prog/g' \
 stderr.txt > stderr.sed], [0], [], [])
 
-AT_CHECK([diff reference_stderr stderr.sed], [0], [], [])
+AT_CHECK([$DIFF reference_stderr stderr.sed], [0], [], [])
 
 AT_CHECK([$COMPILE -fdump=ALL -fno-dump prog.cob sub2.cob], [0], [], [])
 
@@ -10998,7 +10998,7 @@ X is 000005441
 AT_CHECK([$SED -e 's/Started by .*prog.exe/Started by .\/prog/g' \
 stderr.txt > stderr.sed], [0], [], [])
 
-AT_CHECK([diff reference_stderr stderr.sed], [0], [], [])
+AT_CHECK([$DIFF reference_stderr stderr.sed], [0], [], [])
 
 AT_CHECK([$COMPILE -fdump=FD,LS prog.cob sub2.cob -o prog_fdls], [0], [], [])
 
@@ -11080,7 +11080,7 @@ AT_CHECK([$SED -e 's/compiled ... .. .... ..:..:../compiled MMM DD YYYY HH:MM:SS
                    s/Started by .*prog_fdls.exe/Started by .\/prog_fdls/g' \
 tstdump_fdls.dump > tstdump.sed], [0], [], [])
 
-AT_CHECK([diff reference tstdump.sed], [0], [], [])
+AT_CHECK([$DIFF reference tstdump.sed], [0], [], [])
 
 AT_CHECK([$COMPILE -fdump=ALL -fno-dump=LO,WS,SC prog.cob sub2.cob -o prog_allfdls], [0], [], [])
 
@@ -11102,7 +11102,7 @@ tstdump_allfdls.dump > tstdump.sed], [0], [], [])
 AT_CHECK([$SED -e 's/prog_fdls/prog_allfdls/' \
 reference > reference_all], [0], [], [])
 
-AT_CHECK([diff reference_all tstdump.sed], [0], [], [])
+AT_CHECK([$DIFF reference_all tstdump.sed], [0], [], [])
 
 # CHECKME @ Ron: The result is likely wrong, please verify later
 #AT_CHECK([$COMPILE -fdump=LS prog.cob sub2.cob -fsticky-linkage -o prog_ls_sticky], [0], [], [])
@@ -11165,7 +11165,7 @@ AT_CHECK([diff reference_all tstdump.sed], [0], [], [])
 #AT_CHECK([$SED -e 's/compiled ... .. .... ..:..:../compiled MMM DD YYYY HH:MM:SS/g' \
 #tstdump_ls_sticky.dump > tstdump.sed], [0], [], [])
 #
-#AT_CHECK([diff reference tstdump.sed], [0], [], [])
+#AT_CHECK([$DIFF reference tstdump.sed], [0], [], [])
 
 AT_CLEANUP
 
@@ -11441,7 +11441,7 @@ AT_CHECK([test "$COB_HAS_64_BIT_POINTER" = "yes"], [0], [], [],
   AT_CHECK([$SED -e 's/_$//' reference_tmpl > reference], [0], [], [])
 )
 
-AT_CHECK([diff reference dumpall.sed], [0], [], [])
+AT_CHECK([$DIFF reference dumpall.sed], [0], [], [])
 
 AT_CLEANUP
 
@@ -13402,12 +13402,12 @@ This is sent to PRINTER PRINT
 This is also sent to PRINTER PRINT
 ])
 
-AT_CHECK([diff reference prt.log], [0], [], [],
+AT_CHECK([$DIFF reference prt.log], [0], [], [],
 
 # Previous test "failed" --> check if EOL of PIPE is the issue
 
 AT_CHECK([$SED -e 's/PIPE.\r/PIPE./g' prt.log > prt2.log], [0], [], [])
-AT_CHECK([diff reference prt2.log], [0], [], [])
+AT_CHECK([$DIFF reference prt2.log], [0], [], [])
 )
 
 AT_CAPTURE_FILE([punch.out])
@@ -13417,7 +13417,7 @@ AT_DATA([reference],
 This is also sent to SYSPUNCH PRINT
 ])
 
-AT_CHECK([diff reference punch.out], [0], [], [])
+AT_CHECK([$DIFF reference punch.out], [0], [], [])
 
 AT_CLEANUP
 
diff --git a/tests/testsuite.src/run_reportwriter.at b/tests/testsuite.src/run_reportwriter.at
index 78d781e23..dc9552027 100644
--- a/tests/testsuite.src/run_reportwriter.at
+++ b/tests/testsuite.src/run_reportwriter.at
@@ -112,7 +112,7 @@ PF
 RF
 ])
 
-AT_CHECK([diff reference report.txt], [0], [], [])
+AT_CHECK([$DIFF reference report.txt], [0], [], [])
 
 AT_CLEANUP
 
@@ -181,7 +181,7 @@ AT_DATA([reference], [
 
 ])
 
-AT_CHECK([diff reference report.txt], [0], [], [])
+AT_CHECK([$DIFF reference report.txt], [0], [], [])
 
 AT_CLEANUP
 
@@ -250,7 +250,7 @@ AT_DATA([reference], [
 
 ])
 
-AT_CHECK([diff reference report.txt], [0], [], [])
+AT_CHECK([$DIFF reference report.txt], [0], [], [])
 
 AT_CLEANUP
 
@@ -319,7 +319,7 @@ AT_CAPTURE_FILE([report.txt])
 
 AT_DATA([reference], [])
 
-AT_CHECK([diff reference report.txt], [0], [], [])
+AT_CHECK([$DIFF reference report.txt], [0], [], [])
 
 AT_CLEANUP
 
@@ -380,7 +380,7 @@ goodbye                        <--->
 
 ])
 
-AT_CHECK([diff reference report.txt], [0])
+AT_CHECK([$DIFF reference report.txt], [0])
 
 AT_CLEANUP
 
@@ -452,7 +452,7 @@ goodbye                        <--->
 
 ])
 
-AT_CHECK([diff reference report.txt], [0])
+AT_CHECK([$DIFF reference report.txt], [0])
 
 AT_CLEANUP
 
@@ -767,7 +767,7 @@ CUST. NO.     CUST. NAME     DEPT.    ITEM NO.    ITEM COST
 
 ])
 
-AT_CHECK([diff reference report.txt], [0], [], [])
+AT_CHECK([$DIFF reference report.txt], [0], [], [])
 
 AT_CLEANUP
 
@@ -1120,7 +1120,7 @@ CUST. NO.     CUST. NAME     DEPT.    ITEM NO.    ITEM COST    DISCT. %    DISCT
 
 ])
 
-AT_CHECK([diff reference report.txt], [0], [], [])
+AT_CHECK([$DIFF reference report.txt], [0], [], [])
 
 AT_CLEANUP
 
@@ -1490,7 +1490,7 @@ CUST. NO.     CUST. NAME     DEPT.    ITEM NO.    ITEM COST    DISCT. %    DISCT
 
 ])
 
-AT_CHECK([diff reference report.txt], [0], [], [])
+AT_CHECK([$DIFF reference report.txt], [0], [], [])
 
 AT_CLEANUP
 
@@ -1790,7 +1790,7 @@ CUST. NO.     CUST. NAME                          ITEM COST                DISCT
 
 ])
 
-AT_CHECK([diff reference report.txt], [0], [], [])
+AT_CHECK([$DIFF reference report.txt], [0], [], [])
 
 AT_CLEANUP
 
@@ -2206,7 +2206,7 @@ AT_DATA([reference], [                          D I S T R I C T   S A L E S   R
 
 ])
 
-AT_CHECK([diff reference report.txt], [0], [], [])
+AT_CHECK([$DIFF reference report.txt], [0], [], [])
 
 AT_CLEANUP
 
@@ -2887,7 +2887,7 @@ DEPARTMENT NUMBER:  25 MAINTENANCE
                                     $17,208.00 100%   $1,006.78 100%   $2,456.42 100%      $80.00 100%    $13,843.92 100%
 ])
 
-AT_CHECK([diff reference report.txt], [0], [], [])
+AT_CHECK([$DIFF reference report.txt], [0], [], [])
 
 AT_CLEANUP
 
@@ -3055,7 +3055,7 @@ Ln  --ID--     --------Name--------   Major *-*      +Odd+  +Even+
 
 ])
 
-AT_CHECK([diff reference report.txt], [0])
+AT_CHECK([$DIFF reference report.txt], [0])
 
 AT_CLEANUP
 
@@ -3207,7 +3207,7 @@ AT_DATA([reference], [
 
 ])
 
-AT_CHECK([diff reference report.txt], [0], [], [])
+AT_CHECK([$DIFF reference report.txt], [0], [], [])
 
 AT_CLEANUP
 
@@ -3555,7 +3555,7 @@ AT_DATA([reference], [                                           CUSTOMER ORDER
 
 ])
 
-AT_CHECK([diff reference report.txt], [0], [], [])
+AT_CHECK([$DIFF reference report.txt], [0], [], [])
 
 AT_CLEANUP
 
@@ -3784,7 +3784,7 @@ AT_DATA([reference], [
 
 ])
 #" <- fix code highlighting
-AT_CHECK([diff reference report.txt], [0], [], [])
+AT_CHECK([$DIFF reference report.txt], [0], [], [])
 
 AT_CLEANUP
 
@@ -3978,7 +3978,7 @@ AT_DATA([reference], [
                              -+* End of Page *+-      ************        *************       **************
 ])
 
-AT_CHECK([diff reference report.txt], [0], [], [])
+AT_CHECK([$DIFF reference report.txt], [0], [], [])
 
 AT_CLEANUP
 
@@ -4106,7 +4106,7 @@ C        3rd Detail 2
 
 ])
 
-AT_CHECK([diff reference report.txt], [0], [], [])
+AT_CHECK([$DIFF reference report.txt], [0], [], [])
 
 AT_CLEANUP
 
@@ -4210,7 +4210,7 @@ Tag1 *Tag2 **Tag1 *Tag2 **Tag1 *Tag2 **
 
 ])
 
-AT_CHECK([diff reference report.txt], [0])
+AT_CHECK([$DIFF reference report.txt], [0])
 
 AT_CLEANUP
 
@@ -4427,8 +4427,8 @@ Hi-Q:
 Hi-Q:
 ])
 
-AT_CHECK([diff reference report_var.txt], [0])
-AT_CHECK([diff reference report_lit.txt], [0])
+AT_CHECK([$DIFF reference report_var.txt], [0])
+AT_CHECK([$DIFF reference report_lit.txt], [0])
 
 AT_CLEANUP
 
@@ -4573,7 +4573,7 @@ Hi-Q:
 Hi-Q:
 ])
 
-AT_CHECK([diff reference tstdmrp.txt], [0], [], [])
+AT_CHECK([$DIFF reference tstdmrp.txt], [0], [], [])
 
 AT_CLEANUP
 
@@ -4639,7 +4639,7 @@ goodbye                       <--->
 
 ])
 
-AT_CHECK([diff reference report.txt], [0])
+AT_CHECK([$DIFF reference report.txt], [0])
 
 AT_CLEANUP
 
@@ -4699,7 +4699,7 @@ AT_CAPTURE_FILE([report.txt])
 
 AT_DATA([reference], [])
 
-AT_CHECK([diff reference report.txt], [0])
+AT_CHECK([$DIFF reference report.txt], [0])
 
 AT_CLEANUP
 
@@ -4753,7 +4753,7 @@ AT_CAPTURE_FILE([report.txt])
 
 AT_DATA([reference], [])
 
-AT_CHECK([diff reference report.txt], [0])
+AT_CHECK([$DIFF reference report.txt], [0])
 
 AT_CLEANUP
 
@@ -9076,7 +9076,7 @@ IN150202   20150202                          OR150216          016  ITEM_NUMBER_
 
 ])
 
-AT_CHECK([diff reference report.txt], [0])
+AT_CHECK([$DIFF reference report.txt], [0])
 
 AT_CLEANUP
 
@@ -9338,7 +9338,7 @@ AT_DATA([reference], [                           STARK TECHNOLOGIES MONTHLY REPO
 
 ])
 
-AT_CHECK([diff reference report.txt], [0])
+AT_CHECK([$DIFF reference report.txt], [0])
 
 AT_CLEANUP
 
@@ -9512,7 +9512,7 @@ VarQ:
 VarQ:
 ])
 
-AT_CHECK([diff reference tstdmrp.txt], [0], [], [])
+AT_CHECK([$DIFF reference tstdmrp.txt], [0], [], [])
 
 AT_CLEANUP
 
diff --git a/tests/testsuite.src/syn_definition.at b/tests/testsuite.src/syn_definition.at
index 5f43cdc3e..5e54358ea 100644
--- a/tests/testsuite.src/syn_definition.at
+++ b/tests/testsuite.src/syn_definition.at
@@ -2514,7 +2514,7 @@ SIZE  TYPE           LVL  NAME                           PICTURE
 
 ])
 
-AT_CHECK([diff prog-32.lst symbols.lst], [0], [], [])
+AT_CHECK([$DIFF prog-32.lst symbols.lst], [0], [], [])
 
 ] , [
 
@@ -2571,7 +2571,7 @@ SIZE  TYPE           LVL  NAME                           PICTURE
 
 ])
 
-AT_CHECK([diff prog-64.lst symbols.lst], [0], [], [])
+AT_CHECK([$DIFF prog-64.lst symbols.lst], [0], [], [])
 
 ])