diff --git a/defs/gmake.mk b/defs/gmake.mk
index 11e677a2d1..7dd24cfdb4 100644
--- a/defs/gmake.mk
+++ b/defs/gmake.mk
@@ -360,6 +360,10 @@ spec/bundler/%: PHONY
 spec/bundler: test-bundler-parallel
 	$(Q)$(NULLCMD)
 
+# workaround to avoid matching non ruby files with "spec/%/" under GNU make 3.81
+spec/%_spec.c spec/%_spec.bundle:
+	$(NOOP)
+
 spec/%/ spec/%_spec.rb: programs exts PHONY
 	+$(RUNRUBY) -r./$(arch)-fake $(srcdir)/spec/mspec/bin/mspec-run -B $(srcdir)/spec/default.mspec $(SPECOPTS) $(patsubst %,$(srcdir)/%,$@)