diff --git a/Makefile.am b/Makefile.am
index e5ae9f23..6fa61aa6 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -79,6 +79,7 @@ libglnx_srcpath := $(srcdir)/libglnx
 libglnx_cflags := \
 	$(BASE_CFLAGS) \
 	"-I$(libglnx_srcpath)" \
+	-std=gnu99 \
 	$(HIDDEN_VISIBILITY_CFLAGS) \
 	$(NULL)
 libglnx_libs := $(BASE_LIBS)