diff --git a/Makefile.am.inc b/Makefile.am.inc
index 96a791a..fd68a25 100644
--- a/Makefile.am.inc
+++ b/Makefile.am.inc
@@ -1,2 +1,2 @@
-AM_CFLAGS = -Wall -Werror -Wextra -Wwrite-strings -Wno-unused-parameter -std=c99 -D_GNU_SOURCE -D_REENTRANT
+AM_CFLAGS = -Wall -Werror -Wextra -Wwrite-strings -Wno-unused-parameter -std=gnu99 -D_GNU_SOURCE -D_REENTRANT