diff --git a/ports/windows/Makefile b/ports/windows/Makefile
index 489ba15c64..7753fa25d4 100644
--- a/ports/windows/Makefile
+++ b/ports/windows/Makefile
@@ -26,8 +26,8 @@ FROZEN_MANIFEST ?= variants/manifest.py
 PROG ?= micropython
 
 # qstr definitions (must come before including py.mk)
-QSTR_DEFS = ../unix/qstrdefsport.h
-QSTR_GLOBAL_DEPENDENCIES = $(VARIANT_DIR)/mpconfigvariant.h
+QSTR_DEFS += ../unix/qstrdefsport.h
+QSTR_GLOBAL_DEPENDENCIES += $(VARIANT_DIR)/mpconfigvariant.h
 
 # include py core make definitions
 include $(TOP)/py/py.mk