diff --git a/gopmod/classfile.go b/gopmod/classfile.go
index 502d461..a91d8a9 100644
--- a/gopmod/classfile.go
+++ b/gopmod/classfile.go
@@ -18,6 +18,7 @@ package gopmod
 
 import (
 	"errors"
+	"path"
 	"syscall"
 
 	"github.com/goplus/mod/modcache"
@@ -32,7 +33,7 @@ type Project = modfile.Project
 
 var (
 	SpxProject = &Project{
-		Ext:      ".gmx",
+		Ext:      ".spx",
 		Class:    "Game",
 		Works:    []*Class{{Ext: ".spx", Class: "Sprite"}},
 		PkgPaths: []string{"github.com/goplus/spx", "math"},
@@ -45,9 +46,18 @@ var (
 
 // -----------------------------------------------------------------------------
 
-func (p *Module) ClassKind(ext string) (isWork, isProj bool) {
+func (p *Module) ClassKind(fname string) (isProj, ok bool) {
+	ext := path.Ext(fname)
 	if c, ok := p.projects[ext]; ok {
-		isWork, isProj = c.Kind(ext)
+		for _, w := range c.Works {
+			if w.Ext == ext {
+				if ext != c.Ext || fname != "main"+ext {
+					return false, true
+				}
+				break
+			}
+		}
+		return true, true
 	}
 	return
 }
@@ -68,6 +78,7 @@ func (p *Module) ImportClasses(importClass ...func(c *Project)) (err error) {
 		impcls = importClass[0]
 	}
 	p.importClass(SpxProject, impcls)
+	p.projects[".gmx"] = SpxProject // old style
 	if c := p.Project; c != nil {
 		p.importClass(c, impcls)
 	}
diff --git a/modfile/rule.go b/modfile/rule.go
index 2f34997..464faa3 100644
--- a/modfile/rule.go
+++ b/modfile/rule.go
@@ -80,18 +80,6 @@ type Class struct {
 	Syntax *Line
 }
 
-func (p *Project) Kind(ext string) (isWork, isProj bool) {
-	for _, w := range p.Works {
-		if w.Ext == ext {
-			isWork = true
-		}
-	}
-	if p.Ext == ext {
-		isProj = true
-	}
-	return
-}
-
 // A VersionInterval represents a range of versions with upper and lower bounds.
 // Intervals are closed: both bounds are included. When Low is equal to High,
 // the interval may refer to a single version ('v1.2.3') or an interval
diff --git a/modfile/rule_test.go b/modfile/rule_test.go
index 20c3bad..91b6727 100644
--- a/modfile/rule_test.go
+++ b/modfile/rule_test.go
@@ -91,16 +91,6 @@ func TestMustQuote(t *testing.T) {
 
 // -----------------------------------------------------------------------------
 
-func TestKind(t *testing.T) {
-	proj := &Project{Works: []*Class{{Ext: ".spx"}}, Ext: ".spx"}
-	isWork, isProj := proj.Kind(".spx")
-	if !isWork || !isProj {
-		t.Fatal("proj.Kind:", isWork, isProj)
-	}
-}
-
-// -----------------------------------------------------------------------------
-
 var addGopTests = []struct {
 	desc    string
 	in      string