diff --git a/Makefile b/Makefile
index e8793964f..9a69fca8b 100644
--- a/Makefile
+++ b/Makefile
@@ -461,7 +461,7 @@ endif
 
 flat-header: check-env $(BLIS_H_FLAT)
 
-$(BLIS_H_FLAT): $(FRAME_H99_FILES)
+$(BLIS_H_FLAT): $(ALL_H99_FILES)
 ifeq ($(ENABLE_VERBOSE),yes)
 	$(FLATTEN_H) -c -v1 $(BLIS_H_SRC_PATH) $@ "./$(INCLUDE_DIR)" "$(ALL_H99_DIRPATHS)"
 else