diff --git a/C4.puml b/C4.puml
index 800ba06..aa0db07 100644
--- a/C4.puml
+++ b/C4.puml
@@ -656,7 +656,7 @@ $elementSkin
       !endif
     !endif
     !if ($lineThickness != "")
-      !$tagDetails = $tagDetails + thickness " + $lineThickness + ") "
+      !$tagDetails = $tagDetails + "thickness " + $lineThickness + ") "
     !endif
     !if ($tagDetails=="(")
       !$tagDetails = "</size>"