diff --git a/m4/acinclude.m4 b/m4/acinclude.m4
index d236a6bc..4fbbe07e 100644
--- a/m4/acinclude.m4
+++ b/m4/acinclude.m4
@@ -41,9 +41,9 @@ EOF
       dnl GCC
       if test "$GCC" = "yes"; then
         if test -z "$ansi"; then
-          vl_cv_prog_cc_warnings="-Wall"
+          vl_cv_prog_cc_warnings="-Wall -Wextra"
         else
-          vl_cv_prog_cc_warnings="-Wall -ansi -pedantic"
+          vl_cv_prog_cc_warnings="-Wall -Wextra -ansi -pedantic"
         fi
 
       dnl Most compilers print some kind of a version string with some command