diff --git a/lib/asn1/Makefile.am b/lib/asn1/Makefile.am
index 55b13544c..02356bfc8 100644
--- a/lib/asn1/Makefile.am
+++ b/lib/asn1/Makefile.am
@@ -145,7 +145,7 @@ check_gen_template_LDADD = \
 	libasn1.la \
 	$(LIB_roken)
 
-check_gen_CFLAGS = -DIMPLICIT_TAGGING_WORKS
+check_gen_CPPFLAGS = -DIMPLICIT_TAGGING_WORKS
 check_gen_LDADD = \
 	libasn1.la \
 	$(LIB_roken)