diff --git a/src/calibre/gui2/convert/structure_detection.ui b/src/calibre/gui2/convert/structure_detection.ui
index e4414473f5..2e97c0d3ca 100644
--- a/src/calibre/gui2/convert/structure_detection.ui
+++ b/src/calibre/gui2/convert/structure_detection.ui
@@ -28,7 +28,11 @@
     </widget>
    </item>
    <item row="1" column="1">
-    <widget class="QComboBox" name="opt_chapter_mark"/>
+    <widget class="QComboBox" name="opt_chapter_mark">
+     <property name="minimumContentsLength">
+      <number>20</number>
+     </property>
+    </widget>
    </item>
    <item row="2" column="0">
     <widget class="QCheckBox" name="opt_remove_first_image">
diff --git a/src/calibre/gui2/convert/xexp_edit.ui b/src/calibre/gui2/convert/xexp_edit.ui
index 1b0196a8a1..f98eb8b1b8 100644
--- a/src/calibre/gui2/convert/xexp_edit.ui
+++ b/src/calibre/gui2/convert/xexp_edit.ui
@@ -43,6 +43,15 @@
          <height>0</height>
         </size>
        </property>
+       <property name="maximumSize">
+        <size>
+         <width>500</width>
+         <height>16777215</height>
+        </size>
+       </property>
+       <property name="minimumContentsLength">
+        <number>30</number>
+       </property>
       </widget>
      </item>
     </layout>