diff --git a/t/Makefile.am b/t/Makefile.am
index d983825..96c03c6 100644
--- a/t/Makefile.am
+++ b/t/Makefile.am
@@ -37,7 +37,7 @@ TESTS =
 # c++ header test
 TESTS += t_cxx
 t_cxx_SOURCES = t_cxx.cc
-t_cxx_CPPFLAGS = $(AM_CPPFLAGS)
+t_cxx_CPPFLAGS =
 t_cxx_LDADD =
 if CRYB_CIPHER
 t_cxx_CPPFLAGS += -DWITH_CRYB_CIPHER