diff --git a/tests/tbs/tb0634.pp b/tests/tbs/tb0634.pp
index a6ec0c9216..bf4983ac6a 100644
--- a/tests/tbs/tb0634.pp
+++ b/tests/tbs/tb0634.pp
@@ -16,5 +16,8 @@ begin
   s := Concat(s1, ' ', s2, ' ', s3, ' ', s4);
   if s <> 'Hello Free Pascal World' then
     Halt(3);
+  s := Concat(Concat(s1, ' ', s2), ' ', Concat(s3, ' ', s4));
+  if s <> 'Hello Free Pascal World' then
+    Halt(4);
   Writeln('ok');
 end.