diff --git a/Makefile-tests.am b/Makefile-tests.am
index 03e50b9b..517f713b 100644
--- a/Makefile-tests.am
+++ b/Makefile-tests.am
@@ -28,8 +28,8 @@ EXTRA_DIST += \
 # include the builddir in $PATH so we find our just-built ostree
 # binary.
 TESTS_ENVIRONMENT += OT_TESTS_DEBUG=1 \
-	GI_TYPELIB_PATH=$$(cd $(top_builddir) && pwd) \
-	LD_LIBRARY_PATH=$$(cd $(top_builddir)/.libs && pwd) \
+	GI_TYPELIB_PATH=$$(cd $(top_builddir) && pwd)$${GI_TYPELIB_PATH:+:$$GI_TYPELIB_PATH} \
+	LD_LIBRARY_PATH=$$(cd $(top_builddir)/.libs && pwd)$${LD_LIBRARY_PATH:+:$${LD_LIBRARY_PATH}} \
 	PATH=$$(cd $(top_builddir)/tests && pwd):$${PATH} \
 	$(NULL)