diff --git a/pylib/gyp/generator/ninja.py b/pylib/gyp/generator/ninja.py
index b66e674a..cfe3c49a 100644
--- a/pylib/gyp/generator/ninja.py
+++ b/pylib/gyp/generator/ninja.py
@@ -1221,7 +1221,7 @@ def WriteSourcesForArch(
                 command = "cc_s"
             elif (
                 self.flavor == "win"
-                and ext == "asm"
+                and ext in ("asm", "S")
                 and not self.msvs_settings.HasExplicitAsmRules(spec)
             ):
                 command = "asm"