diff --git a/Makefile.am b/Makefile.am
index 86cdbf963999a0b73474811af71459faa8496e1d..28694335a92c385a433a64442bb9966b0d51f04a 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -5,7 +5,8 @@ lib_LTLIBRARIES = libopus.la
 
 DIST_SUBDIRS = doc
 
-INCLUDES = -I$(top_srcdir)/include -I$(top_srcdir)/celt -I$(top_srcdir)/silk -I$(top_srcdir)/silk/float -I$(top_srcdir)/silk/fixed
+AM_CPPFLAGS = -I$(top_srcdir)/include -I$(top_srcdir)/celt -I$(top_srcdir)/silk \
+              -I$(top_srcdir)/silk/float -I$(top_srcdir)/silk/fixed
 
 include celt_sources.mk
 include silk_sources.mk