[2.0][DDC-355] Fixed. Patch provided by Christian Heinrich.

lib/Doctrine/ORM/Mapping/ClassMetadataInfo.php

@@ -1435,11 +1435,16 @@ class ClassMetadataInfo
             $this->discriminatorMap[$value] = $className;
             if ($this->name == $className) {
                 $this->discriminatorValue = $value;
-            } else if (is_subclass_of($className, $this->name)) {
+            } else {
+                if ( ! class_exists($className)) {
+                    throw MappingException::invalidClassInDiscriminatorMap($className, $this->name);
+                }
+                if (is_subclass_of($className, $this->name)) {
                     $this->subClasses[] = $className;
                 }
             }
         }
+    }
 
     /**
      * Gets the discriminator value of this class.

lib/Doctrine/ORM/Mapping/MappingException.php

@@ -170,4 +170,19 @@ class MappingException extends \Doctrine\ORM\ORMException
     {
         return new self('The annotation driver needs to have a directory path');
     }
+
+    /**
+     * Throws an exception that indicates that a class used in a discriminator map does not exist.
+     * An example would be an outdated (maybe renamed) classname.
+     *
+     * @param string $className The class that could not be found
+     * @param string $owningClass The class that declares the discriminator map.
+     * @return self
+     */
+    public static function invalidClassInDiscriminatorMap($invalidClass, $owningClass) {
+        return new self(
+            "Entity class '$className' used in the discriminator map of class '$owningClass' ".
+            "does not exist."
+        );
+    }
 }