diff --git a/lib/core/settings.py b/lib/core/settings.py
index bf71f1774..005f6ec78 100644
--- a/lib/core/settings.py
+++ b/lib/core/settings.py
@@ -342,3 +342,7 @@ DEFAULT_TOR_PORTS = (8118, 8123)
 
 # Percentage below which comparison engine could have problems
 LOW_TEXT_PERCENT = 20
+
+# These MySQL keywords can't go (alone) into versioned comment form (/*!...*/)
+# Reference: http://dev.mysql.com/doc/refman/5.1/en/function-resolution.html
+IGNORE_SPACE_AFFECTED_KEYWORDS = ("CAST", "COUNT", "EXTRACT", "GROUP_CONCAT", "MAX", "MID", "MIN", "SESSION_USER", "SUBSTR", "SUBSTRING", "SUM", "SYSTEM_USER", "TRIM")
diff --git a/tamper/versionedkeywords.py b/tamper/versionedkeywords.py
index 4cc61b874..fe80149a8 100644
--- a/tamper/versionedkeywords.py
+++ b/tamper/versionedkeywords.py
@@ -12,6 +12,7 @@ import re
 from lib.core.common import randomRange
 from lib.core.data import kb
 from lib.core.enums import PRIORITY
+from lib.core.settings import IGNORE_SPACE_AFFECTED_KEYWORDS
 
 __priority__ = PRIORITY.NORMAL
 
@@ -23,7 +24,7 @@ def tamper(payload):
 
     def process(match):
         word = match.group('word')
-        if word.upper() in kb.keywords and word.upper() not in ["CAST", "COUNT"]: # keywords that can't be commented out
+        if word.upper() in kb.keywords and word.upper() not in IGNORE_SPACE_AFFECTED_KEYWORDS:
             return match.group().replace(word, "/*!%s*/" % word)
         else:
             return match.group()