diff --git a/lib/zip_replace_data.c b/lib/zip_replace_data.c
index 1db8ba1..78a358b 100644
--- a/lib/zip_replace_data.c
+++ b/lib/zip_replace_data.c
@@ -57,9 +57,11 @@
     case ZIP_CMD_READ:
 	n = len > z->len ? z->len : len;
 
-	memcpy(buf, z->buf, n);
-	z->buf += n;
-	z->len -= n;
+	if (n) {
+	    memcpy(buf, z->buf, n);
+	    z->buf += n;
+	    z->len -= n;
+	}
 
 	return n;