diff --git a/lib/portfolio/caller.php b/lib/portfolio/caller.php
index d5026d8aed1..32ee370670a 100644
--- a/lib/portfolio/caller.php
+++ b/lib/portfolio/caller.php
@@ -448,24 +448,7 @@ abstract class portfolio_caller_base {
         if (in_array($format, $this->supportedformats)) {
             return;
         }
-        $formatobj = portfolio_format_object($format);
-        // TODO look at replacing this code with another call to
-        //$this->supportedformats = portfolio_most_specific_formats($this->supportedformats, $formats);
-        //requires testing forum, which is the only place this is implemented right now
-        foreach ($this->supportedformats as $key => $f) {
-            $f2obj = portfolio_format_object($f);
-            $class = get_class($f2obj);
-            if ($formatobj instanceof $class) {
-                unset($this->supportedformats[$key]);
-            }
-            if ($formatobj->conflicts($f)) {
-                unset($this->supportedformats[$key]);
-            }
-            if ($f2obj->conflicts($format)) {
-                unset($this->supportedformats[$key]);
-            }
-        }
-        $this->supportedformats[] = $format;
+        $this->supportedformats = portfolio_most_specific_formats(array($format), $this->supportedformats);
     }
 
     public function get_mimetype() {
diff --git a/lib/portfoliolib.php b/lib/portfoliolib.php
index 1dda06e2e3e..b71d9ea00f8 100644
--- a/lib/portfoliolib.php
+++ b/lib/portfoliolib.php
@@ -670,31 +670,44 @@ function portfolio_most_specific_formats($specificformats, $generalformats) {
     } else if (empty($generalformats)) {
         return $specificformats;
     }
-    foreach ($specificformats as $f) {
+    $removedformats = array();
+    foreach ($specificformats as $k => $f) {
         // look for something less specific and remove it, ie outside of the inheritance tree of the current formats.
         if (!array_key_exists($f, $allformats)) {
             if (!portfolio_format_is_abstract($f)) {
                 throw new portfolio_button_exception('invalidformat', 'portfolio', $f);
             }
         }
+        if (in_array($f, $removedformats)) {
+            // already been removed from the general list
+            debugging("skipping $f because it was already removed");
+            unset($specificformats[$k]);
+        }
         require_once($CFG->libdir . '/portfolio/formats.php');
         $fobj = new $allformats[$f];
         foreach ($generalformats as $key => $cf) {
+            if (in_array($cf, $removedformats)) {
+                debugging("skipping $cf because it was already removed");
+                continue;
+            }
             $cfclass = $allformats[$cf];
             $cfobj = new $allformats[$cf];
             if ($fobj instanceof $cfclass && $cfclass != get_class($fobj)) {
                 debugging("unsetting $key $cf because it's not specific enough ($f is better)");
                 unset($generalformats[$key]);
+                $removedformats[] = $cf;
                 continue;
             }
             // check for conflicts
             if ($fobj->conflicts($cf)) {
                 debugging("unsetting $key $cf because it conflicts with $f");
                 unset($generalformats[$key]);
+                $removedformats[] = $cf;
                 continue;
             }
             if ($cfobj->conflicts($f)) {
                 debugging("unsetting $key $cf because it reverse-conflicts with $f");
+                $removedformats[] = $cf;
                 unset($generalformats[$key]);
                 continue;
             }