diff --git a/packets.c b/packets.c
index 208370f..5b87940 100644
--- a/packets.c
+++ b/packets.c
@@ -206,7 +206,7 @@ static int resize_ech_ext(char *buffer,
     SHTONA(buffer, ech_offs + 2, ech_sz + inc);
     SHTONA(buffer, pay_offs, pay_sz + inc);
     
-    memmove(buffer + ech_end + inc, buffer + ech_end, n - ech_end);
+    memmove(buffer + ech_end + inc, buffer + ech_end, n - (ech_end + inc));
     return inc;
 }