diff --git a/Makefile.in b/Makefile.in
index 5bb15c760dd..13e96c37d95 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -93,7 +93,7 @@ rust: $(CFG_RUSTC)
 
 define DEF_SUBMODULE_VARS
 DEPS_$(1) =
-CFLAGS_$(1) = -O2
+CFLAGS_$(1) = $$(CFLAGS) 
 # any "done" dummy files must be named libSOMETHING.dummy. 
 #
 # We can't auto-compute this, because some modules have lib* prefix in