Index: exec.c
===================================================================
--- exec.c	(revision 5391)
+++ exec.c	(working copy)
@@ -2068,12 +2068,13 @@
     target_ulong end;
     target_ulong addr;
 
+    if( start + len < start )
+        /* we've wrapped around */
+        return -1;
+
     end = TARGET_PAGE_ALIGN(start+len); /* must do before we loose bits in the next step */
     start = start & TARGET_PAGE_MASK;
 
-    if( end < start )
-        /* we've wrapped around */
-        return -1;
     for(addr = start; addr < end; addr += TARGET_PAGE_SIZE) {
         p = page_find(addr >> TARGET_PAGE_BITS);
         if( !p )