diff --git a/debugger/debugger.pp b/debugger/debugger.pp
index 4d96c5436d..df85256008 100644
--- a/debugger/debugger.pp
+++ b/debugger/debugger.pp
@@ -3628,7 +3628,7 @@ end;
 
 procedure TDBGWatch.SetSlave(const ASlave : TBaseWatch);
 begin
-  Assert(FSlave = nil, 'TDBGWatch.SetSlave already has a slave');
+  Assert((FSlave = nil) or (ASlave = nil), 'TDBGWatch.SetSlave already has a slave');
   FSlave := ASlave;
 end;