diff --git a/lib/outputlib.php b/lib/outputlib.php
index 77ee70ea0e0..5fe61d348db 100644
--- a/lib/outputlib.php
+++ b/lib/outputlib.php
@@ -1646,12 +1646,13 @@ class theme_config {
      *
      * Use this function sparingly and never for icons. For icons use pix_icon or the pix helper in a mustache template.
      *
+     * @deprecated since Moodle 3.3
      * @param string $imagename the name of the icon.
      * @param string $component specification of one plugin like in get_string()
      * @return moodle_url
      */
     public function pix_url($imagename, $component) {
-        debugging('pix_url is deprecated. Use image_url for images and pix_icon for icons.');
+        debugging('pix_url is deprecated. Use image_url for images and pix_icon for icons.', DEBUG_DEVELOPER);
         return $this->image_url($imagename, $component);
     }
 
diff --git a/lib/outputrenderers.php b/lib/outputrenderers.php
index c57bb73bec3..7406646d05b 100644
--- a/lib/outputrenderers.php
+++ b/lib/outputrenderers.php
@@ -253,8 +253,18 @@ class renderer_base {
         return $classes;
     }
 
+    /**
+     * Return the direct URL for an image from the pix folder.
+     *
+     * Use this function sparingly and never for icons. For icons use pix_icon or the pix helper in a mustache template.
+     *
+     * @deprecated since Moodle 3.3
+     * @param string $imagename the name of the icon.
+     * @param string $component specification of one plugin like in get_string()
+     * @return moodle_url
+     */
     public function pix_url($imagename, $component = 'moodle') {
-        debugging('pix_url is deprecated. Use image_url for images and pix_icon for icons.');
+        debugging('pix_url is deprecated. Use image_url for images and pix_icon for icons.', DEBUG_DEVELOPER);
         return $this->page->theme->image_url($imagename, $component);
     }