diff --git a/src/StringLocalizer.cs b/src/StringLocalizer.cs
index 2614b16..e7f3f6e 100644
--- a/src/StringLocalizer.cs
+++ b/src/StringLocalizer.cs
@@ -85,7 +85,7 @@ public string this[string str]
             {
                 try
                 {
-                    return resourceManager.GetString(str);
+                    return resourceManager.GetString(str) ?? str;
                 }
                 catch
                 {