diff --git a/_config/html.yml b/_config/html.yml
index dff94addb..83b30d3db 100644
--- a/_config/html.yml
+++ b/_config/html.yml
@@ -16,7 +16,7 @@ SilverStripe\Core\Injector\Injector:
 
 SilverStripe\Forms\HTMLEditor\TinyMCEConfig:
   image_size_presets:
-    - width: 600,
+    - width: 600
       i18n: SilverStripe\Forms\HTMLEditor\TinyMCEConfig.BEST_FIT
       text: Best fit
       name: bestfit
diff --git a/src/Forms/HTMLEditor/TinyMCEConfig.php b/src/Forms/HTMLEditor/TinyMCEConfig.php
index e7f356fa6..f4bc99dbc 100644
--- a/src/Forms/HTMLEditor/TinyMCEConfig.php
+++ b/src/Forms/HTMLEditor/TinyMCEConfig.php
@@ -694,6 +694,10 @@ class TinyMCEConfig extends HTMLEditorConfig implements i18nEntityProvider
         }
 
         foreach ($settings['image_size_presets'] as &$preset) {
+            if (isset($preset['width'])) {
+                $preset['width'] = (int) $preset['width'];
+            }
+
             if (isset($preset['i18n'])) {
                 $preset['text'] = _t(
                     $preset['i18n'],