diff --git a/system/database/DB_query_builder.php b/system/database/DB_query_builder.php
index 5491b20..5a86ce5 100644
--- a/system/database/DB_query_builder.php
+++ b/system/database/DB_query_builder.php
@@ -679,7 +679,7 @@
 				// value appears not to have been set, assign the test to IS NULL
 				$k .= ' IS NULL';
 			}
-			elseif (preg_match('/\s*(!?=|<>|IS(?:\s+NOT)?)\s*$/i', $k, $match, PREG_OFFSET_CAPTURE))
+			elseif (preg_match('/\s*(!?=|<>|\sIS(?:\s+NOT)?\s)\s*$/i', $k, $match, PREG_OFFSET_CAPTURE))
 			{
 				$k = substr($k, 0, $match[0][1]).($match[1][0] === '=' ? ' IS NULL' : ' IS NOT NULL');
 			}