diff --git a/mongoengine/fields.py b/mongoengine/fields.py
index 866dc7e3..79045898 100644
--- a/mongoengine/fields.py
+++ b/mongoengine/fields.py
@@ -64,7 +64,7 @@ class StringField(BaseField):
                 regex = r'%s$'
             elif op == 'exact':
                 regex = r'^%s$'
-            value = re.compile(regex % value, flags)
+            value = re.compile(regex % re.escape(value), flags)
         return value