diff -ruN libxml2-2.6.21/xmlmemory.c libxml2-2.6.21-fixed/xmlmemory.c
--- libxml2-2.6.21/xmlmemory.c	2005-05-08 13:31:15.000000000 +0200
+++ libxml2-2.6.21-fixed/xmlmemory.c	2005-09-11 11:33:13.631301960 +0200
@@ -409,6 +409,10 @@
     size_t size;
 #endif
 
+    if (!ptr) {
+        goto error;
+    }
+
     if (ptr == (void *) -1) {
 	xmlGenericError(xmlGenericErrorContext,
 	    "trying to free pointer from freed area\n");