diff --git a/src/Horse.Compression.pas b/src/Horse.Compression.pas
index 0fff4b2..cf1ba6e 100644
--- a/src/Horse.Compression.pas
+++ b/src/Horse.Compression.pas
@@ -45,7 +45,7 @@ procedure Middleware(Req: THorseRequest; Res: THorseResponse; Next: {$IF DEFINED
   LContent := Res.Content;
   if (not Assigned(LContent)) or (not LContent.InheritsFrom({$IF DEFINED(FPC)}TJsonData{$ELSE}TJSONValue{$ENDIF})) then
     Exit;
-  if not Req.Headers.Contains(ACCEPT_ENCODING) then
+  if not Req.Headers.ContainsKey(ACCEPT_ENCODING) then
     Exit;
   LAcceptEncoding := Req.Headers[ACCEPT_ENCODING].ToLower;
   if Pos(THorseCompressionType.DEFLATE.ToString, LAcceptEncoding) > 0 then