diff --git a/pkg/mcp/tools_build.go b/pkg/mcp/tools_build.go
index 52576187aa..3d55776942 100644
--- a/pkg/mcp/tools_build.go
+++ b/pkg/mcp/tools_build.go
@@ -20,6 +20,10 @@ var buildTool = &mcp.Tool{
 }
 
 func (s *Server) buildHandler(ctx context.Context, r *mcp.CallToolRequest, input BuildInput) (result *mcp.CallToolResult, output BuildOutput, err error) {
+	if s.readonly && input.Push != nil && *input.Push {
+		err = fmt.Errorf("the server is in read-only mode; set FUNC_ENABLE_MCP_WRITE=true to push images")
+		return
+	}
 	out, err := s.executor.Execute(ctx, "build", input.Args()...)
 	if err != nil {
 		err = fmt.Errorf("%w\n%s", err, string(out))