diff --git a/src/win32.mak b/src/win32.mak
index 4537d0239543..378b437005a8 100644
--- a/src/win32.mak
+++ b/src/win32.mak
@@ -61,6 +61,7 @@
 # fixed model for win32.mak, overridden by win64.mak
 MODEL=32
 BUILD=release
+OS=windows
 
 ##### Directories