diff --git a/lib/attacks/tamper_scripts/url_encode.py b/lib/attacks/tamper_scripts/url_encode.py
index d4c88d7..32eee14 100644
--- a/lib/attacks/tamper_scripts/url_encode.py
+++ b/lib/attacks/tamper_scripts/url_encode.py
@@ -1,7 +1,7 @@
 # coding=utf-8
 
 
-def tamper(payload, **kwargs):
+def tamper(payload, safe="%&=-_", **kwargs):
     encodings = {
         " ": "%20", "!": "%21", '"': "%22", "#": "%23", "$": "%24", "%": "%25", "&": "%26", "'": "%27",
         "(": "%28", ")": "%29", "*": "%2A", "+": "%2B", ",": "%2C", "-": "%2D", ".": "%2E", "/": "%2F",
@@ -35,8 +35,11 @@ def tamper(payload, **kwargs):
     if isinstance(payload, unicode):
         payload = str(payload)
     for char in payload:
-        try:
-            retval += encodings[char]
-        except KeyError:
+        if char not in safe:
+            try:
+                retval += encodings[char]
+            except KeyError:
+                retval += char
+        else:
             retval += char
     return retval