diff --git a/library/bignum.c b/library/bignum.c
index cfaaf5f..d5e799e 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -1550,7 +1550,7 @@
  */
 static void mpi_montg_init( mbedtls_mpi_uint *mm, const mbedtls_mpi *N )
 {
-    *mm = mbedtls_mpi_montg_init( N->p[0] );
+    *mm = mbedtls_mpi_montg_init( N->p );
 }
 
 /** Montgomery multiplication: A = A * B * R^-1 mod N  (HAC 14.36)