diff --git a/library/ecp.c b/library/ecp.c
index ecea591..db36191 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -1046,25 +1046,29 @@
 #define INC_MUL_COUNT
 #endif
 
-#define MOD_MUL( N )    do { MBEDTLS_MPI_CHK( ecp_modp( &N, grp ) ); INC_MUL_COUNT } \
-                        while( 0 )
+#define MOD_MUL( N )                                                    \
+    do                                                                  \
+    {                                                                   \
+        MBEDTLS_MPI_CHK( ecp_modp( &(N), grp ) );                       \
+        INC_MUL_COUNT                                                   \
+    } while( 0 )
 
 /*
  * Reduce a mbedtls_mpi mod p in-place, to use after mbedtls_mpi_sub_mpi
  * N->s < 0 is a very fast test, which fails only if N is 0
  */
-#define MOD_SUB( N )                                \
-    while( N.s < 0 && mbedtls_mpi_cmp_int( &N, 0 ) != 0 )   \
-        MBEDTLS_MPI_CHK( mbedtls_mpi_add_mpi( &N, &N, &grp->P ) )
+#define MOD_SUB( N )                                                    \
+    while( (N).s < 0 && mbedtls_mpi_cmp_int( &(N), 0 ) != 0 )           \
+        MBEDTLS_MPI_CHK( mbedtls_mpi_add_mpi( &(N), &(N), &grp->P ) )
 
 /*
  * Reduce a mbedtls_mpi mod p in-place, to use after mbedtls_mpi_add_mpi and mbedtls_mpi_mul_int.
  * We known P, N and the result are positive, so sub_abs is correct, and
  * a bit faster.
  */
-#define MOD_ADD( N )                                \
-    while( mbedtls_mpi_cmp_mpi( &N, &grp->P ) >= 0 )        \
-        MBEDTLS_MPI_CHK( mbedtls_mpi_sub_abs( &N, &N, &grp->P ) )
+#define MOD_ADD( N )                                                    \
+    while( mbedtls_mpi_cmp_mpi( &(N), &grp->P ) >= 0 )                  \
+        MBEDTLS_MPI_CHK( mbedtls_mpi_sub_abs( &(N), &(N), &grp->P ) )
 
 #if defined(ECP_SHORTWEIERSTRASS)
 /*