diff --git a/exec-obsolete.h b/exec-obsolete.h
index c412be9..22e0ba5 100644
--- a/exec-obsolete.h
+++ b/exec-obsolete.h
@@ -77,17 +77,18 @@
 }
 
 static inline void cpu_physical_memory_mask_dirty_range(ram_addr_t start,
-                                                        int length,
+                                                        ram_addr_t length,
                                                         int dirty_flags)
 {
-    int i, mask, len;
+    int mask;
     uint8_t *p;
+    ram_addr_t addr, end;
 
-    len = length >> TARGET_PAGE_BITS;
+    end = start + length;
     mask = ~dirty_flags;
     p = ram_list.phys_dirty + (start >> TARGET_PAGE_BITS);
-    for (i = 0; i < len; i++) {
-        p[i] &= mask;
+    for (addr = start; addr <= end; addr += TARGET_PAGE_SIZE) {
+        *p++ &= mask;
     }
 }