diff --git a/redash/settings/helpers.py b/redash/settings/helpers.py
index 2f3f2f657a..98946d81e4 100644
--- a/redash/settings/helpers.py
+++ b/redash/settings/helpers.py
@@ -1,5 +1,4 @@
 import os
-import simplejson
 
 
 def fix_assets_path(path):
@@ -19,8 +18,15 @@ def set_from_string(s):
     return set(array_from_string(s))
 
 
-def parse_boolean(str):
-    return simplejson.loads(str.lower())
+def parse_boolean(s):
+    """Takes a string and returns the equivalent as a boolean value."""
+    s = s.strip().lower()
+    if s in ('yes', 'true', 'on', '1'):
+        return True
+    elif s in ('no', 'false', 'off', '0', 'none'):
+        return False
+    else:
+        raise ValueError('Invalid boolean value %r' % s)
 
 
 def int_or_none(value):