diff --git a/libsecret/tests/Makefile.am b/libsecret/tests/Makefile.am
index 92c528d..c5a6a29 100644
--- a/libsecret/tests/Makefile.am
+++ b/libsecret/tests/Makefile.am
@@ -1,5 +1,9 @@
 include $(top_srcdir)/Makefile.decl
 
+# test-vala-unstable depends on the mock vapi,
+# and I'm not sure how we can add that dependency.
+.NOTPARALLEL:
+
 INCLUDES = \
 	-I$(top_srcdir) \
 	-I$(top_srcdir)/libsecret \