diff --git a/Makefile.am.common b/Makefile.am.common
index b00473d..49019ec 100644
--- a/Makefile.am.common
+++ b/Makefile.am.common
@@ -1,2 +1,2 @@
-AM_CFLAGS = -I$(top_srcdir)/include -I$(top_srcdir)/include/compat
-AM_CPPFLAGS = -DLIBRESSL_INTERNAL
+AM_CFLAGS =
+AM_CPPFLAGS = -I$(top_srcdir)/include -I$(top_srcdir)/include/compat -DLIBRESSL_INTERNAL
diff --git a/crypto/Makefile.am b/crypto/Makefile.am
index bed4712..e1e785d 100644
--- a/crypto/Makefile.am
+++ b/crypto/Makefile.am
@@ -1,8 +1,8 @@
 include $(top_srcdir)/Makefile.am.common
 
-AM_CFLAGS += -I$(top_srcdir)/crypto/asn1
-AM_CFLAGS += -I$(top_srcdir)/crypto/evp
-AM_CFLAGS += -I$(top_srcdir)/crypto/modes
+AM_CPPFLAGS += -I$(top_srcdir)/crypto/asn1
+AM_CPPFLAGS += -I$(top_srcdir)/crypto/evp
+AM_CPPFLAGS += -I$(top_srcdir)/crypto/modes
 
 lib_LTLIBRARIES = libcrypto.la
 
@@ -14,7 +14,8 @@ EXTRA_DIST += compat/strcasecmp.c
 
 libcrypto_la_LDFLAGS = -version-info @LIBCRYPTO_VERSION@ -no-undefined
 libcrypto_la_LIBADD = libcompat.la libcompatnoopt.la
-libcrypto_la_CPPFLAGS = -DLIBRESSL_INTERNAL
+libcrypto_la_CPPFLAGS = $(AM_CPPFLAGS)
+libcrypto_la_CPPFLAGS += -DLIBRESSL_INTERNAL
 libcrypto_la_CPPFLAGS += -DOPENSSL_NO_HW_PADLOCK
 if OPENSSL_NO_ASM
 libcrypto_la_CPPFLAGS += -DOPENSSL_NO_ASM