diff --git a/subdir-rules.mk b/subdir-rules.mk
index 0995a7449..24eff4f56 100644
--- a/subdir-rules.mk
+++ b/subdir-rules.mk
@@ -22,5 +22,5 @@
 # generator_built is defined in individual Makefiles
 $(generator_built): $(top_builddir)/generator/stamp-generator
 $(top_builddir)/generator/stamp-generator: force
-	$(MAKE) -C $(top_builddir)/generator stamp-generator
-
+	! test -f $(top_builddir)/generator/Makefile || \
+	  $(MAKE) -C $(top_builddir)/generator stamp-generator