Add missing gtest include
diff --git a/guththila/tests/Makefile.am b/guththila/tests/Makefile.am
index d180486..de4493a 100644
--- a/guththila/tests/Makefile.am
+++ b/guththila/tests/Makefile.am
@@ -21,7 +21,8 @@
 
 AM_CPPFLAGS = -I$(top_builddir)/include \
 				-I ../../util/include \
-				-I ../../axiom/include
+				-I ../../axiom/include \
+				-I $(GTEST_DIR)/include
 
 test_guththila_LDADD = \
 				 $(top_builddir)/src/libguththila.la \