diff --git a/binding/form_mapping.go b/binding/form_mapping.go
index 80b1d15..ec78bfe 100644
--- a/binding/form_mapping.go
+++ b/binding/form_mapping.go
@@ -15,7 +15,7 @@ import (
 	"github.com/gin-gonic/gin/internal/json"
 )
 
-var errUnknownType = errors.New("Unknown type")
+var errUnknownType = errors.New("unknown type")
 
 func mapUri(ptr interface{}, m map[string][]string) error {
 	return mapFormByTag(ptr, m, "uri")