diff --git a/src/porchlight/templates/admin/user_detail.html b/src/porchlight/templates/admin/user_detail.html
index 147adc7..f65717e 100644
--- a/src/porchlight/templates/admin/user_detail.html
+++ b/src/porchlight/templates/admin/user_detail.html
@@ -29,7 +29,7 @@
         </div>
         <div>
             <label for="phone_number">Phone number</label>
-            <input type="tel" id="phone_number" name="phone_number" value="{{ target_user.phone_number or '' }}" maxlength="50">
+            <input type="tel" id="phone_number" name="phone_number" value="{{ target_user.phone_number or '' }}" maxlength="50" pattern="\+[0-9 ]+" title="International format: +46701234567">
         </div>
         <div>
             <label for="picture">Picture URL</label>
diff --git a/src/porchlight/templates/manage/profile.html b/src/porchlight/templates/manage/profile.html
index 71a3d47..a47858a 100644
--- a/src/porchlight/templates/manage/profile.html
+++ b/src/porchlight/templates/manage/profile.html
@@ -33,7 +33,7 @@
             </div>
             <div>
                 <label for="phone_number">Phone number</label>
-                <input type="tel" id="phone_number" name="phone_number" value="{{ user.phone_number or '' }}" maxlength="50" autocomplete="tel">
+                <input type="tel" id="phone_number" name="phone_number" value="{{ user.phone_number or '' }}" maxlength="50" autocomplete="tel" pattern="\+[0-9 ]+" title="International format: +46701234567">
             </div>
             <div>
                 <label for="picture">Picture URL</label>