diff --git a/packages/fcl-base/src/streamex.pp b/packages/fcl-base/src/streamex.pp
index 0a4388c00d..df03bb1a4b 100644
--- a/packages/fcl-base/src/streamex.pp
+++ b/packages/fcl-base/src/streamex.pp
@@ -626,7 +626,7 @@ end;
 
 constructor TStringWriter.Create(aBuilder: TStringBuilder);
 begin
-  FBuilder := TStringBuilder.Create;
+  FBuilder := aBuilder;
   FFreeBuilder := False;
 end;