diff --git a/uc.c b/uc.c
index aa553e8b..92c0d72a 100644
--- a/uc.c
+++ b/uc.c
@@ -553,8 +553,8 @@ uc_err uc_mem_map(uch handle, uint64_t address, size_t size)
         return UC_ERR_UCH;
 
     // align to 8KB boundary
-    map_begin[map_count] = address & (~ (8*1024));
-    s = (size + 8*1024 - 1) & (~ (8*1024));
+    map_begin[map_count] = address & (~ (8*1024 - 1));
+    s = (size + 8*1024 - 1) & (~ (8*1024 - 1));
     map_end[map_count] = s + map_begin[map_count];
     uc->memory_map(uc, map_begin[map_count], s);
     map_count++;