--- a/libregex/Makefile.am
+++ b/libregex/Makefile.am
@@ -1,6 +1,6 @@
 SUBDIRS = . tests
 
-AM_CPPFLAGS = -I ${top_srcdir}/libutil++
+AM_CPPFLAGS = -I ${top_srcdir}/libutil++ @OP_CPPFLAGS@
 AM_CXXFLAGS = @OP_CXXFLAGS@
 
 noinst_LIBRARIES = libop_regex.a