diff --git a/blocks/login/block_login.php b/blocks/login/block_login.php
index 56831f9b727..5699ba65186 100644
--- a/blocks/login/block_login.php
+++ b/blocks/login/block_login.php
@@ -94,7 +94,7 @@ class block_login extends block_base {
             }
 
             $this->content->text .= '<div class="form-group">';
-            $this->content->text .= '<input type="submit" class="btn btn-primary" value="'.get_string('login').'" />';
+            $this->content->text .= '<input type="submit" class="btn btn-primary btn-block" value="'.get_string('login').'" />';
             $this->content->text .= '</div>';
 
             $this->content->text .= "</form>\n";