diff --git a/src/aof.c b/src/aof.c
index 89f17aba..6fb969fa 100644
--- a/src/aof.c
+++ b/src/aof.c
@@ -970,7 +970,7 @@ int rewriteAppendOnlyFileBackground(void) {
 
             if (private_dirty) {
                 redisLog(REDIS_NOTICE,
-                    "AOF rewrite: %lu MB of memory used by copy-on-write",
+                    "AOF rewrite: %zu MB of memory used by copy-on-write",
                     private_dirty/(1024*1024));
             }
             exitFromChild(0);
diff --git a/src/rdb.c b/src/rdb.c
index 2581c007..512dc3cb 100644
--- a/src/rdb.c
+++ b/src/rdb.c
@@ -737,7 +737,7 @@ int rdbSaveBackground(char *filename) {
 
             if (private_dirty) {
                 redisLog(REDIS_NOTICE,
-                    "RDB: %lu MB of memory used by copy-on-write",
+                    "RDB: %zu MB of memory used by copy-on-write",
                     private_dirty/(1024*1024));
             }
         }