diff --git a/makerom/aes_keygen.c b/makerom/aes_keygen.c
index ffaa4d9..c993410 100644
--- a/makerom/aes_keygen.c
+++ b/makerom/aes_keygen.c
@@ -140,7 +140,7 @@ void ctr_aes_keygen(const uint8_t *x, const uint8_t *y, uint8_t *key)
 	n128_xor(x_rot, y, key_xy);
 
 	// key_xyc = key_xy + KEYGEN_CONST
-	n128_add(key_xy, KEYGEN_CONST, key);
+	n128_add(key_xy, KEYGEN_CONST, key_xyc);
 
 	n128_rrot(key_xyc, 41, key);
 }
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