diff --git a/genkeys.go b/genkeys.go
index a0f33fde8..b84f1647c 100644
--- a/genkeys.go
+++ b/genkeys.go
@@ -437,7 +437,7 @@ func (k Key) String() string {
 	{{range $index, $name := .DriverKeyNames}}case Key{{$name}}:
 		return {{$name | printf "Key%s" | printf "%q"}}
 	{{end}}}
-	panic(fmt.Sprintf("driver: invalid key: %v", k))
+	panic(fmt.Sprintf("driver: invalid key: %d", k))
 }
 `
 
diff --git a/internal/driver/keys.go b/internal/driver/keys.go
index 3994c0f11..4a49970b4 100644
--- a/internal/driver/keys.go
+++ b/internal/driver/keys.go
@@ -340,5 +340,5 @@ func (k Key) String() string {
 	case KeyUp:
 		return "KeyUp"
 	}
-	panic(fmt.Sprintf("driver: invalid key: %v", k))
+	panic(fmt.Sprintf("driver: invalid key: %d", k))
 }