diff --git a/changelog.d/14625.bugfix b/changelog.d/14625.bugfix
new file mode 100644
index 000000000000..a4d1216690ec
--- /dev/null
+++ b/changelog.d/14625.bugfix
@@ -0,0 +1 @@
+Fix html templates to load images only on HTTPS. Contributed by @ashfame.
diff --git a/synapse/res/templates/_base.html b/synapse/res/templates/_base.html
index 46439fce6aa6..4b5cc7bcb62a 100644
--- a/synapse/res/templates/_base.html
+++ b/synapse/res/templates/_base.html
@@ -13,13 +13,13 @@
 <body>
 <header class="mx_Header">
     {% if app_name == "Riot" %}
-        <img src="http://riot.im/img/external/riot-logo-email.png" width="83" height="83" alt="[Riot]"/>
+        <img src="https://riot.im/img/external/riot-logo-email.png" width="83" height="83" alt="[Riot]"/>
     {% elif app_name == "Vector" %}
-        <img src="http://matrix.org/img/vector-logo-email.png" width="64" height="83" alt="[Vector]"/>
+        <img src="https://matrix.org/img/vector-logo-email.png" width="64" height="83" alt="[Vector]"/>
     {% elif app_name == "Element" %}
         <img src="https://static.element.io/images/email-logo.png" width="83" height="83" alt="[Element]"/>
     {% else %}
-        <img src="http://matrix.org/img/matrix-120x51.png" width="120" height="51" alt="[matrix]"/>
+        <img src="https://matrix.org/img/matrix-120x51.png" width="120" height="51" alt="[matrix]"/>
     {% endif %}
 </header>
 
diff --git a/synapse/res/templates/notice_expiry.html b/synapse/res/templates/notice_expiry.html
index 406397aaca76..f62038e111cc 100644
--- a/synapse/res/templates/notice_expiry.html
+++ b/synapse/res/templates/notice_expiry.html
@@ -21,13 +21,13 @@
                     </td>
                     <td class="logo">
                         {% if app_name == "Riot" %}
-                            <img src="http://riot.im/img/external/riot-logo-email.png" width="83" height="83" alt="[Riot]"/>
+                            <img src="https://riot.im/img/external/riot-logo-email.png" width="83" height="83" alt="[Riot]"/>
                         {% elif app_name == "Vector" %}
-                            <img src="http://matrix.org/img/vector-logo-email.png" width="64" height="83" alt="[Vector]"/>
+                            <img src="https://matrix.org/img/vector-logo-email.png" width="64" height="83" alt="[Vector]"/>
                         {% elif app_name == "Element" %}
                             <img src="https://static.element.io/images/email-logo.png" width="83" height="83" alt="[Element]"/>
                         {% else %}
-                            <img src="http://matrix.org/img/matrix-120x51.png" width="120" height="51" alt="[matrix]"/>
+                            <img src="https://matrix.org/img/matrix-120x51.png" width="120" height="51" alt="[matrix]"/>
                         {% endif %}
                     </td>
                 </tr>
diff --git a/synapse/res/templates/notif_mail.html b/synapse/res/templates/notif_mail.html
index 2add9dd859ce..7da0fff5e946 100644
--- a/synapse/res/templates/notif_mail.html
+++ b/synapse/res/templates/notif_mail.html
@@ -22,13 +22,13 @@
                     </td>
                     <td class="logo">
                         {%- if app_name == "Riot" %}
-                            <img src="http://riot.im/img/external/riot-logo-email.png" width="83" height="83" alt="[Riot]"/>
+                            <img src="https://riot.im/img/external/riot-logo-email.png" width="83" height="83" alt="[Riot]"/>
                         {%- elif app_name == "Vector" %}
-                            <img src="http://matrix.org/img/vector-logo-email.png" width="64" height="83" alt="[Vector]"/>
+                            <img src="https://matrix.org/img/vector-logo-email.png" width="64" height="83" alt="[Vector]"/>
                         {%- elif app_name == "Element" %}
                             <img src="https://static.element.io/images/email-logo.png" width="83" height="83" alt="[Element]"/>
                         {%- else %}
-                            <img src="http://matrix.org/img/matrix-120x51.png" width="120" height="51" alt="[matrix]"/>
+                            <img src="https://matrix.org/img/matrix-120x51.png" width="120" height="51" alt="[matrix]"/>
                         {%- endif %}
                     </td>
                 </tr>
