diff --git a/lib/src/widgets/toolbar.dart b/lib/src/widgets/toolbar.dart
index a53bae78..65cdadcf 100644
--- a/lib/src/widgets/toolbar.dart
+++ b/lib/src/widgets/toolbar.dart
@@ -202,7 +202,7 @@ class QuillToolbar extends StatelessWidget implements PreferredSizeWidget {
                 ),
             ],
             onSelected: (newSize) {
-              if (newSize != null) {
+              if (newSize != null) && (newSize > 0) {
                 controller
                     .formatSelection(Attribute.fromKeyValue('size', newSize));
               }