diff --git a/common/lib/capa/capa/responsetypes.py b/common/lib/capa/capa/responsetypes.py
index ab5eaf950c..df98f62fc5 100644
--- a/common/lib/capa/capa/responsetypes.py
+++ b/common/lib/capa/capa/responsetypes.py
@@ -746,7 +746,7 @@ class NumericalResponse(LoncapaResponse):
                                            id=xml.get('id'))[0]
             self.tolerance = contextualize_text(self.tolerance_xml, context)
         except Exception:
-            self.tolerance = 0
+            self.tolerance = '0'
         try:
             self.answer_id = xml.xpath('//*[@id=$id]//textline/@id',
                                        id=xml.get('id'))[0]
diff --git a/common/lib/capa/capa/util.py b/common/lib/capa/capa/util.py
index 75acf657e8..75bd9fb5bc 100644
--- a/common/lib/capa/capa/util.py
+++ b/common/lib/capa/capa/util.py
@@ -11,7 +11,7 @@ def compare_with_tolerance(v1, v2, tol):
 
      - v1    :  student result (number)
      - v2    :  instructor result (number)
-     - tol   :  tolerance (string or number)
+     - tol   :  tolerance (string representing a number)
 
     '''
     relative = tol.endswith('%')