diff --git a/ui/composer-headerbar.ui b/ui/composer-headerbar.ui
index fb0d8624..ef8cbb24 100644
--- a/ui/composer-headerbar.ui
+++ b/ui/composer-headerbar.ui
@@ -1,15 +1,9 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <interface>
-  <requires lib="gtk+" version="3.14"/>
-  <object class="GtkImage" id="send_image">
-    <property name="visible">True</property>
-    <property name="can_focus">False</property>
-    <property name="icon_name">mail-send-symbolic</property>
-  </object>
+  <requires lib="gtk+" version="3.20"/>
   <template class="ComposerHeaderbar" parent="GtkHeaderBar">
     <property name="visible">True</property>
     <property name="can_focus">False</property>
-    <property name="show_close_button">False</property>
     <child>
       <object class="GtkBox" id="detach_start">
         <property name="visible">True</property>
@@ -19,18 +13,25 @@
             <property name="visible">True</property>
             <property name="can_focus">True</property>
             <property name="focus_on_click">False</property>
-            <property name="margin_end">6</property>
-            <property name="relief">GTK_RELIEF_NONE</property>
-            <property name="action_name">cmh.detach</property>
-            <property name="always_show_image">True</property>
+            <property name="receives_default">False</property>
             <property name="tooltip_text" translatable="yes">Detach (Ctrl+D)</property>
+            <property name="margin_end">6</property>
+            <property name="action_name">cmh.detach</property>
+            <property name="relief">none</property>
+            <property name="always_show_image">True</property>
             <child>
               <object class="GtkImage" id="detach_start_image">
+                <property name="can_focus">False</property>
+                <property name="pixel_size">16</property>
                 <property name="icon_name">detach-symbolic</property>
-                <property name="pixel-size">16</property>
               </object>
             </child>
           </object>
+          <packing>
+            <property name="expand">False</property>
+            <property name="fill">True</property>
+            <property name="position">0</property>
+          </packing>
         </child>
         <child>
           <object class="GtkSeparator" id="detach_start_separator">
@@ -38,6 +39,11 @@
             <property name="can_focus">False</property>
             <property name="orientation">vertical</property>
           </object>
+          <packing>
+            <property name="expand">False</property>
+            <property name="fill">True</property>
+            <property name="position">1</property>
+          </packing>
         </child>
       </object>
     </child>
@@ -46,74 +52,101 @@
         <property name="visible">True</property>
         <property name="can_focus">True</property>
         <property name="focus_on_click">False</property>
+        <property name="receives_default">False</property>
+        <property name="tooltip_text" translatable="yes">Attach File (Ctrl+T)</property>
         <property name="action_name">cmh.add-attachment</property>
         <property name="always_show_image">True</property>
-        <property name="tooltip_text" translatable="yes">Attach File (Ctrl+T)</property>
         <child>
           <object class="GtkImage" id="new_message_attach_image">
             <property name="visible">True</property>
+            <property name="can_focus">False</property>
+            <property name="pixel_size">16</property>
             <property name="icon_name">mail-attachment-symbolic</property>
-            <property name="pixel-size">16</property>
           </object>
         </child>
       </object>
+      <packing>
+        <property name="position">1</property>
+      </packing>
     </child>
     <child>
       <object class="GtkBox" id="conversation_attach_buttons">
         <property name="visible">True</property>
         <property name="can_focus">False</property>
-        <style>
-          <class name="linked"/>
-        </style>
         <child>
           <object class="GtkButton" id="conversation_attach_new_button">
             <property name="visible">True</property>
             <property name="can_focus">True</property>
             <property name="focus_on_click">False</property>
+            <property name="receives_default">False</property>
+            <property name="tooltip_text" translatable="yes">Attach File (Ctrl+T)</property>
             <property name="action_name">cmh.add-attachment</property>
             <property name="always_show_image">True</property>
-            <property name="tooltip_text" translatable="yes">Attach File (Ctrl+T)</property>
             <child>
               <object class="GtkImage" id="conversation_attach_new_image">
                 <property name="visible">True</property>
+                <property name="can_focus">False</property>
+                <property name="pixel_size">16</property>
                 <property name="icon_name">mail-attachment-symbolic</property>
-                <property name="pixel-size">16</property>
               </object>
             </child>
           </object>
+          <packing>
+            <property name="expand">False</property>
+            <property name="fill">True</property>
+            <property name="position">0</property>
+          </packing>
         </child>
         <child>
           <object class="GtkButton" id="conversation_attach_original_button">
             <property name="visible">True</property>
             <property name="can_focus">True</property>
             <property name="focus_on_click">False</property>
+            <property name="receives_default">False</property>
+            <property name="tooltip_text" translatable="yes">Include Original Attachments</property>
             <property name="action_name">cmh.add-original-attachments</property>
             <property name="always_show_image">True</property>
-            <property name="tooltip_text" translatable="yes">Include Original Attachments</property>
             <child>
               <object class="GtkImage" id="conversation_attach_original_image">
                 <property name="visible">True</property>
+                <property name="can_focus">False</property>
+                <property name="pixel_size">16</property>
                 <property name="icon_name">edit-copy-symbolic</property>
-                <property name="pixel-size">16</property>
               </object>
             </child>
           </object>
+          <packing>
+            <property name="expand">False</property>
+            <property name="fill">True</property>
+            <property name="position">1</property>
+          </packing>
         </child>
+        <style>
+          <class name="linked"/>
+        </style>
       </object>
+      <packing>
+        <property name="position">2</property>
+      </packing>
     </child>
     <child>
       <object class="GtkButton" id="recipients_button">
         <property name="visible">True</property>
         <property name="can_focus">True</property>
-        <property name="relief">GTK_RELIEF_NONE</property>
         <property name="focus_on_click">False</property>
+        <property name="receives_default">False</property>
+        <property name="relief">none</property>
         <child>
           <object class="GtkLabel" id="recipients_label">
             <property name="visible">True</property>
+            <property name="can_focus">False</property>
             <property name="ellipsize">end</property>
           </object>
         </child>
       </object>
+      <packing>
+        <property name="position">3</property>
+      </packing>
     </child>
     <child>
       <object class="GtkBox" id="detach_end">
@@ -125,94 +158,123 @@
             <property name="can_focus">False</property>
             <property name="orientation">vertical</property>
           </object>
+          <packing>
+            <property name="expand">False</property>
+            <property name="fill">True</property>
+            <property name="position">0</property>
+          </packing>
         </child>
         <child>
           <object class="GtkButton" id="detach_end_button">
             <property name="visible">True</property>
             <property name="can_focus">True</property>
             <property name="focus_on_click">False</property>
-            <property name="margin_start">6</property>
-            <property name="relief">GTK_RELIEF_NONE</property>
-            <property name="action_name">cmh.detach</property>
-            <property name="always_show_image">True</property>
+            <property name="receives_default">False</property>
             <property name="tooltip_text" translatable="yes">Detach (Ctrl+D)</property>
+            <property name="margin_start">6</property>
+            <property name="action_name">cmh.detach</property>
+            <property name="relief">none</property>
+            <property name="always_show_image">True</property>
             <child>
               <object class="GtkImage" id="detach_end_image">
                 <property name="visible">True</property>
+                <property name="can_focus">False</property>
+                <property name="pixel_size">16</property>
                 <property name="icon_name">detach-symbolic</property>
-                <property name="pixel-size">16</property>
               </object>
             </child>
           </object>
+          <packing>
+            <property name="expand">False</property>
+            <property name="fill">True</property>
+            <property name="position">1</property>
+          </packing>
         </child>
       </object>
       <packing>
         <property name="pack_type">end</property>
+        <property name="position">4</property>
       </packing>
     </child>
     <child>
       <object class="GtkButton" id="send_button">
+        <property name="label" translatable="yes">_Send</property>
         <property name="visible">True</property>
         <property name="can_focus">True</property>
         <property name="focus_on_click">False</property>
-        <property name="action_name">cmh.send</property>
-        <property name="always_show_image">True</property>
-        <property name="image">send_image</property>
-        <property name="use_underline">True</property>
+        <property name="receives_default">False</property>
         <property name="tooltip_text" translatable="yes">Send (Ctrl+Enter)</property>
-        <property name="label" translatable="yes">_Send</property>
+        <property name="action_name">cmh.send</property>
+        <property name="use_underline">True</property>
+        <property name="always_show_image">True</property>
         <style>
           <class name="suggested-action"/>
         </style>
       </object>
       <packing>
         <property name="pack_type">end</property>
+        <property name="position">5</property>
       </packing>
     </child>
     <child>
       <object class="GtkBox" id="close_buttons">
         <property name="visible">True</property>
         <property name="can_focus">False</property>
-        <style>
-          <class name="linked"/>
-        </style>
         <child>
           <object class="GtkButton" id="discard_and_close_button">
             <property name="visible">True</property>
             <property name="can_focus">True</property>
             <property name="focus_on_click">False</property>
+            <property name="receives_default">False</property>
+            <property name="tooltip_text" translatable="yes">Discard and Close</property>
             <property name="action_name">cmh.close-and-discard</property>
             <property name="always_show_image">True</property>
-            <property name="tooltip_text" translatable="yes">Discard and Close</property>
             <child>
               <object class="GtkImage" id="discard_and_close_image">
                 <property name="visible">True</property>
+                <property name="can_focus">False</property>
+                <property name="pixel_size">16</property>
                 <property name="icon_name">user-trash-symbolic</property>
-                <property name="pixel-size">16</property>
               </object>
             </child>
           </object>
+          <packing>
+            <property name="expand">False</property>
+            <property name="fill">True</property>
+            <property name="position">0</property>
+          </packing>
         </child>
         <child>
           <object class="GtkButton" id="save_and_close_button">
             <property name="visible">True</property>
             <property name="can_focus">True</property>
             <property name="focus_on_click">False</property>
+            <property name="receives_default">False</property>
+            <property name="tooltip_text" translatable="yes">Save and Close</property>
             <property name="action_name">cmh.close-and-save</property>
             <property name="always_show_image">True</property>
-            <property name="tooltip_text" translatable="yes">Save and Close</property>
             <child>
               <object class="GtkImage" id="save_and_close_image">
                 <property name="visible">True</property>
+                <property name="can_focus">False</property>
+                <property name="pixel_size">16</property>
                 <property name="icon_name">document-save-symbolic</property>
-                <property name="pixel-size">16</property>
               </object>
             </child>
           </object>
+          <packing>
+            <property name="expand">False</property>
+            <property name="fill">True</property>
+            <property name="position">1</property>
+          </packing>
         </child>
+        <style>
+          <class name="linked"/>
+        </style>
       </object>
       <packing>
         <property name="pack_type">end</property>
+        <property name="position">6</property>
       </packing>
     </child>
   </template>