diff --git a/httpp/Makefile.am b/httpp/Makefile.am
index 453a76f..7240fd2 100644
--- a/httpp/Makefile.am
+++ b/httpp/Makefile.am
@@ -7,6 +7,7 @@ noinst_HEADERS = httpp.h
 
 libicehttpp_la_SOURCES = httpp.c
 libicehttpp_la_CFLAGS = @XIPH_CFLAGS@
+AM_CPPFLAGS = @XIPH_CPPFLAGS@
 
 INCLUDES = -I$(srcdir)/..