diff --git a/extensions/WinResTarget_activex.mk b/extensions/WinResTarget_activex.mk
index 7b9c1374f639..df6d833a7938 100644
--- a/extensions/WinResTarget_activex.mk
+++ b/extensions/WinResTarget_activex.mk
@@ -41,7 +41,7 @@ $(eval $(call gb_WinResTarget_add_file,activex_res,extensions/source/activex/so_
 
 $(eval $(call gb_WinResTarget_set_defs,activex_res,\
 	$$(DEFS) \
-	-DSO_ACTIVEX_TLB_DIR=$(call gb_Helper_convert_native,$(WORKDIR)/CustomTarget/extensions/source/activex/idl) \
+	-DSO_ACTIVEX_TLB_DIR=$(subst /,\\,$(subst $(call gb_Helper_convert_native,$(SRCDIR)),../../..,$(call gb_Helper_convert_native,$(WORKDIR)/CustomTarget/extensions/source/activex/idl))) \
 ))
 
 # I suppose this dep is not really necessary, because it should always