diff --git a/library/ecp.c b/library/ecp.c
index 538d2cf..24cd21b 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -2930,9 +2930,9 @@
 
 #if defined(MBEDTLS_ECP_MONTGOMERY_ENABLED)
 #if defined(MBEDTLS_ECP_DP_CURVE25519_ENABLED)
-#define ECP_MPI_INIT(_s, _n, _p) { .s = (_s), .n = (_n), .p = (mbedtls_mpi_uint *) (_p) }
+#define ECP_MPI_INIT(_p, _n) { .p = (mbedtls_mpi_uint *) (_p), .s = 1, .n = (_n) }
 #define ECP_MPI_INIT_ARRAY(x)   \
-    ECP_MPI_INIT(1, sizeof(x) / sizeof(mbedtls_mpi_uint), x)
+    ECP_MPI_INIT(x, sizeof(x) / sizeof(mbedtls_mpi_uint))
 /*
  * Constants for the two points other than 0, 1, -1 (mod p) in
  * https://cr.yp.to/ecdh.html#validate