diff --git a/tests/examples/gtk/Makefile.am b/tests/examples/gtk/Makefile.am
index 15636d9..cd7962d 100644
--- a/tests/examples/gtk/Makefile.am
+++ b/tests/examples/gtk/Makefile.am
@@ -15,6 +15,7 @@
 gtkglsink_CFLAGS = \
 	$(GST_PLUGINS_BAD_CFLAGS) \
 	$(GST_PLUGINS_BASE_CFLAGS) \
+	$(GST_GL_CFLAGS) \
 	$(GST_CFLAGS) \
 	$(GL_CFLAGS) \
 	$(GTK3_CFLAGS)