diff --git a/compiler/symdef.pas b/compiler/symdef.pas
index 6fb51dcdb0..7e79a1d799 100644
--- a/compiler/symdef.pas
+++ b/compiler/symdef.pas
@@ -4367,7 +4367,7 @@ implementation
 
        for i:=0 to prot.ImplementedInterfaces.count-1 do
          begin
-           result:=is_related_protocol(tobjectdef(prot.ImplementedInterfaces[i]),d);
+           result:=is_related_protocol(TImplementedInterface(prot.ImplementedInterfaces[i]).intfdef,d);
            if result then
              exit;
          end;