diff --git a/src/Microsoft.Windows.CsWin32/Generator.cs b/src/Microsoft.Windows.CsWin32/Generator.cs
index 54063e27..7ba418d0 100644
--- a/src/Microsoft.Windows.CsWin32/Generator.cs
+++ b/src/Microsoft.Windows.CsWin32/Generator.cs
@@ -579,7 +579,8 @@ public bool TryGenerateConstant(string name)
         {
             var starterNamespace = NamespaceDeclaration(ParseName(this.Namespace));
 
-            const string FilenamePattern = "{0}.cs";
+            // .g.cs because the resulting files are not user-created.
+            const string FilenamePattern = "{0}.g.cs";
             var results = new Dictionary<string, NamespaceDeclarationSyntax>(StringComparer.OrdinalIgnoreCase);
 
             if (this.options.EmitSingleFile)