Index: Zend/zend_vm_execute.h
===================================================================
RCS file: /repository/ZendEngine2/zend_vm_execute.h,v
retrieving revision 1.4
diff -u -r1.4 zend_vm_execute.h
--- Zend/zend_vm_execute.h	3 Nov 2004 07:11:49 -0000	1.4
+++ Zend/zend_vm_execute.h	29 Nov 2004 13:56:15 -0000
@@ -20880,9 +20880,12 @@
 		} else if ((*container)->type == IS_STRING) { /* string offsets */
 			switch (opline->extended_value) {
 				case ZEND_ISSET:
-					if (offset->value.lval < Z_STRLEN_PP(container)) {
+					if (offset->value.lval >= 0 && offset->value.lval < Z_STRLEN_PP(container)) {
 						result = 1;
 					}
+					else {
+						result = 0;
+					}
 					break;
 				case ZEND_ISEMPTY:
 					if (offset->value.lval < Z_STRLEN_PP(container) && Z_STRVAL_PP(container)[offset->value.lval] != '0') {