diff --git a/src/cmd/go/help_test.go b/src/cmd/go/help_test.go
index abfc3db993..3e1d817ca5 100644
--- a/src/cmd/go/help_test.go
+++ b/src/cmd/go/help_test.go
@@ -6,6 +6,8 @@ package main_test
 
 import (
 	"bytes"
+	"go/format"
+	diffpkg "internal/diff"
 	"os"
 	"testing"
 
@@ -23,11 +25,17 @@ func TestDocsUpToDate(t *testing.T) {
 	buf := new(bytes.Buffer)
 	// Match the command in mkalldocs.sh that generates alldocs.go.
 	help.Help(buf, []string{"documentation"})
-	data, err := os.ReadFile("alldocs.go")
+	internal := buf.Bytes()
+	internal, err := format.Source(internal)
+	if err != nil {
+		t.Fatalf("gofmt docs: %v", err)
+	}
+	alldocs, err := os.ReadFile("alldocs.go")
 	if err != nil {
 		t.Fatalf("error reading alldocs.go: %v", err)
 	}
-	if !bytes.Equal(data, buf.Bytes()) {
-		t.Errorf("alldocs.go is not up to date; run mkalldocs.sh to regenerate it")
+	if !bytes.Equal(internal, alldocs) {
+		t.Errorf("alldocs.go is not up to date; run mkalldocs.sh to regenerate it\n%s",
+			diffpkg.Diff("go help documentation | gofmt", internal, "alldocs.go", alldocs))
 	}
 }