diff --git a/erc721/server.go b/erc721/server.go
index 9fc7592..37e18d1 100644
--- a/erc721/server.go
+++ b/erc721/server.go
@@ -37,9 +37,9 @@ type MetadataServer struct {
 
 	// Metadata and Image are responsible for returning a token's metadata and
 	// image, respectively (surprise, surprise!). If Contract is non-nil, the
-	// token is guaranteed to exist if Metadata/Image is called. Only 200, 404,
-	// and 500 are allowed as HTTP codes, and these will be propagated to the
-	// end user.
+	// token is guaranteed to exist if Metadata/Image is called. Only 200, 400,
+	// 404 and 500 are allowed as HTTP codes, and these will be propagated to
+	// the end user.
 	Metadata func(Interface, *TokenID, httprouter.Params) (md *Metadata, httpCode int, err error)
 	Image    func(Interface, *TokenID, httprouter.Params) (img io.Reader, contentType string, httpCode int, err error)
 }
@@ -131,6 +131,10 @@ type tokenDataFunc func(Interface, *TokenID, httprouter.Params) (body io.Reader,
 // tokenDataHandler is a generic handler for any token data, abstracting shared
 // logic from the metadata and image handlers.
 func (s *MetadataServer) tokenDataHandler(w http.ResponseWriter, r *http.Request, params httprouter.Params, fnName string, fn tokenDataFunc) error {
+	if fn == nil {
+		return errorf(400, "unsupported method %s", fnName)
+	}
+
 	id, err := s.tokenID(params)
 	if err != nil {
 		return errorf(500, "%T.tokenID(%+v): %v", s, params, err)
@@ -146,7 +150,7 @@ func (s *MetadataServer) tokenDataHandler(w http.ResponseWriter, r *http.Request
 
 	switch code {
 	case 200:
-	case 404, 500:
+	case 400, 404, 500:
 		return errorf(code, "%s", err)
 	default:
 		return errorf(500, "unsupported code %d returned by %s(%s)", code, fnName, id)
diff --git a/erc721/server_test.go b/erc721/server_test.go
index a06bf73..0a63d6d 100644
--- a/erc721/server_test.go
+++ b/erc721/server_test.go
@@ -79,15 +79,22 @@ func TestMetadataServer(t *testing.T) {
 	)
 
 	tests := []struct {
-		Name             string
-		ExternalImageURL string
+		Name                  string
+		ExternalImageURL      string
+		Image                 func(_ Interface, id *TokenID, params httprouter.Params) (io.Reader, string, int, error)
+		wantInternalImageCode int
 	}{
 		{
 			Name: "Internal images",
+			Image: func(_ Interface, id *TokenID, params httprouter.Params) (io.Reader, string, int, error) {
+				return strings.NewReader(fmt.Sprintf("Image %s", id)), imageType, 200, nil
+			},
+			wantInternalImageCode: 200,
 		},
 		{
-			Name:             "External images",
-			ExternalImageURL: "http://foo.bar",
+			Name:                  "External images",
+			ExternalImageURL:      "http://foo.bar",
+			wantInternalImageCode: 400,
 		},
 	}
 
@@ -108,15 +115,17 @@ func TestMetadataServer(t *testing.T) {
 
 					return &md, 200, nil
 				},
-				Image: func(_ Interface, id *TokenID, params httprouter.Params) (io.Reader, string, int, error) {
-					return strings.NewReader(fmt.Sprintf("Image %s", id)), imageType, 200, nil
-				},
+				Image: tt.Image,
 			}
 			baseURL, get := start(t, srv)
 			tokenURL := func(id int) string {
 				// Note the use of %x as we set TokenIDBase to 16.
 				return fmt.Sprintf("%s/metadata/%x", baseURL, id)
 			}
+			internalImageURL := func(id int) string {
+				// Note the use of %x as we set TokenIDBase to 16.
+				return fmt.Sprintf("%s/image/%x", baseURL, id)
+			}
 
 			for id := 0; id < totalSupply; id++ {
 				t.Run(fmt.Sprintf("token %d", id), func(t *testing.T) {
@@ -191,6 +200,15 @@ func TestMetadataServer(t *testing.T) {
 							}
 						})
 					})
+
+					t.Run("internal image code", func(t *testing.T) {
+						path := internalImageURL(id)
+						resp := get(t, path)
+						if got, want := resp.StatusCode, tt.wantInternalImageCode; got != want {
+							t.Errorf("HTTP GET %q: got code %v, want %v", path, got, want)
+						}
+					})
+
 				})
 			}
 
diff --git a/package.json b/package.json
index 905cb51..46c75bc 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@divergencetech/ethier",
-  "version": "0.40.0",
+  "version": "0.40.1",
   "description": "Golang and Solidity SDK to make Ethereum development ethier",
   "main": "\"\"",
   "scripts": {