diff --git a/docs/changelog.rst b/docs/changelog.rst
index 4a55727..7bf7df6 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -1,6 +1,12 @@
 Changelog
 ==========
 
+In git master
+-------------
+
+* Added ``pk_regex`` to the ``PolymorphicParentModelAdmin`` to support non-integer primary keys.
+
+
 Version 0.5.5 (2014-04-29)
 --------------------------
 
diff --git a/polymorphic/admin.py b/polymorphic/admin.py
index ac5a817..2d1d13e 100644
--- a/polymorphic/admin.py
+++ b/polymorphic/admin.py
@@ -102,7 +102,10 @@ class PolymorphicParentModelAdmin(admin.ModelAdmin):
 
     add_type_template = None
     add_type_form = PolymorphicModelChoiceForm
-    
+
+    #: The regular expression to filter the primary key in the URL.
+    #: This accepts only numbers as defensive measure against catch-all URLs.
+    #: If your primary key consists of string values, update this regular expression.
     pk_regex = '(\d+)'