diff --git a/config/opal_check_knem.m4 b/config/opal_check_knem.m4
index a45547a47e6..65ac21b028e 100644
--- a/config/opal_check_knem.m4
+++ b/config/opal_check_knem.m4
@@ -31,11 +31,15 @@ AC_DEFUN([OPAL_CHECK_KNEM],[
 
     opal_check_knem_CPPFLAGS_save="${CPPFLAGS}"
 
-    AS_IF([test -n "${with_knem}" -a "${with_knem}" != "yes" -a "${with_knem}" != "no"],
-          [$1_CPPFLAGS="-I${with_knem}/include"
-           CPPFLAGS="$CPPFLAGS ${$1_CPPFLAGS}"])
+    AS_IF([test -n "${with_knem}" -a "${with_knem}" = "no"],
+          [opal_check_knem_happy="no"],
+          [opal_check_knem_happy="yes"])
 
-    AC_CHECK_HEADER([knem_io.h], [opal_check_knem_happy="yes"], [opal_check_knem_happy="no"])
+    AS_IF([test "${opal_check_knem_happy}" = "yes"],
+          [AS_IF([test -a "${with_knem}" != "yes"],
+                 [$1_CPPFLAGS="-I${with_knem}/include"
+                  CPPFLAGS="$CPPFLAGS ${$1_CPPFLAGS}"])
+           AC_CHECK_HEADER([knem_io.h], [opal_check_knem_happy="yes"], [opal_check_knem_happy="no"])])
 
     # need at least version 0x0000000b
     AS_IF([test "$opal_check_knem_happy" = "yes"],