diff --git a/wmail/configure.in b/wmail/configure.in
index 7054c52..9b36dbf 100644
--- a/wmail/configure.in
+++ b/wmail/configure.in
@@ -55,8 +55,8 @@ dnl Enable Debugging?
 AC_ARG_ENABLE(debug,
                 [  --enable-debug	  enable debugging ],, enable_debug=no)
 if test "$enable_debug" = yes; then
-	CPPFLAGS="$CPPFLAGS -DDEBUG"
-	CFLAGS="$CFLAGS -Wall -g"
+	CPPFLAGS="$CPPFLAGS -DDEBUG -D_XOPEN_SOURCE=600"
+	CFLAGS="$CFLAGS -std=c99 -pedantic -Wall -Wextra -g"
 fi
 
 dnl Use delt's pixmaps instead of the default ones?