diff --git a/progit/hooks/__init__.py b/progit/hooks/__init__.py
index 9f35565..69be6b0 100644
--- a/progit/hooks/__init__.py
+++ b/progit/hooks/__init__.py
@@ -10,10 +10,29 @@
 
 import os
 import shutil
+import wtforms
 
 from progit import APP, get_repo_path
 
 
+class RequiredIf(wtforms.validators.Required):
+        """ Wtforms validator setting a field as required if another field
+        has a value.
+        """
+
+        def __init__(self, other_field_name, *args, **kwargs):
+            self.other_field_name = other_field_name
+            super(RequiredIf, self).__init__(*args, **kwargs)
+
+        def __call__(self, form, field):
+            other_field = form._fields.get(self.other_field_name)
+            if other_field is None:
+                raise Exception(
+                    'no field named "%s" in form' % self.other_field_name)
+            if bool(other_field.data):
+                super(RequiredIf, self).__call__(form, field)
+
+
 class BaseHook(object):
     ''' Base class for progit's hooks. '''