diff --git a/Misc/NEWS.d/next/Build/2025-08-26-21-18-32.gh-issue-128042.5voC8H.rst b/Misc/NEWS.d/next/Build/2025-08-26-21-18-32.gh-issue-128042.5voC8H.rst
new file mode 100644
index 00000000000000..fd85e0fee2162b
--- /dev/null
+++ b/Misc/NEWS.d/next/Build/2025-08-26-21-18-32.gh-issue-128042.5voC8H.rst
@@ -0,0 +1 @@
+``./configure`` now warns when ``--enable-optimizations`` and ``CFLAGS=-O0`` are both set, suggesting removing ``-O0`` from ``CFLAGS`` for optimal performance.  Patch by Taegyun Kim.
diff --git a/configure b/configure
index 568db406dbc67b..bdeab8a6d126a3 100755
--- a/configure
+++ b/configure
@@ -8407,6 +8407,13 @@ fi
 
 
 if test "$Py_OPT" = 'true' ; then
+  # Check for conflicting CFLAGS=-O0 and --enable-optimizations
+  case "$CFLAGS" in
+    *-O0*)
+      { printf "%s\n" "$as_me:${as_lineno-$LINENO}: WARNING: CFLAGS contains -O0 which may conflict with --enable-optimizations. Consider removing -O0 from CFLAGS for optimal performance." >&5
+printf "%s\n" "$as_me: WARNING: CFLAGS contains -O0 which may conflict with --enable-optimizations. Consider removing -O0 from CFLAGS for optimal performance." >&2;}
+      ;;
+  esac
   # Intentionally not forcing Py_LTO='true' here.  Too many toolchains do not
   # compile working code using it and both test_distutils and test_gdb are
   # broken when you do manage to get a toolchain that works with it.  People
diff --git a/configure.ac b/configure.ac
index bbaff7f80352b8..991fa40746be78 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1823,6 +1823,14 @@ fi],
 [AC_MSG_RESULT([no])])
 
 if test "$Py_OPT" = 'true' ; then
+  # Check for conflicting CFLAGS=-O0 and --enable-optimizations
+  case "$CFLAGS" in
+    *-O0*)
+      AC_MSG_WARN([m4_normalize([
+        CFLAGS contains -O0 which may conflict with --enable-optimizations.
+        Consider removing -O0 from CFLAGS for optimal performance.])])
+      ;;
+  esac
   # Intentionally not forcing Py_LTO='true' here.  Too many toolchains do not
   # compile working code using it and both test_distutils and test_gdb are
   # broken when you do manage to get a toolchain that works with it.  People