diff --git a/src/Microsoft.AspNetCore.Mvc.Core/Formatters/FormatFilter.cs b/src/Microsoft.AspNetCore.Mvc.Core/Formatters/FormatFilter.cs
index 03c25c4c0c..c47bb2683e 100644
--- a/src/Microsoft.AspNetCore.Mvc.Core/Formatters/FormatFilter.cs
+++ b/src/Microsoft.AspNetCore.Mvc.Core/Formatters/FormatFilter.cs
@@ -28,7 +28,7 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
         }
 
         /// <inheritdoc />
-        public string GetFormat(ActionContext context)
+        public virtual string GetFormat(ActionContext context)
         {
             object obj;
             if (context.RouteData.Values.TryGetValue("format", out obj))
@@ -159,4 +159,4 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
         {
         }
     }
-}
\ No newline at end of file
+}