diff --git a/library/bignum_mod.c b/library/bignum_mod.c
index ba661e2a0d..ccc5c3bd78 100644
--- a/library/bignum_mod.c
+++ b/library/bignum_mod.c
@@ -136,15 +136,23 @@ cleanup:
     return ret;
 }
 
+static inline void standard_modulus_setup(mbedtls_mpi_mod_modulus *N,
+                                         const mbedtls_mpi_uint *p,
+                                         size_t p_limbs,
+                                         mbedtls_mpi_mod_rep_selector int_rep)
+{
+    N->p = p;
+    N->limbs = p_limbs;
+    N->bits = mbedtls_mpi_core_bitlen(p, p_limbs);
+    N->int_rep = int_rep;
+}
+
 int mbedtls_mpi_mod_modulus_setup(mbedtls_mpi_mod_modulus *N,
                                   const mbedtls_mpi_uint *p,
                                   size_t p_limbs)
 {
     int ret = 0;
-    N->p = p;
-    N->limbs = p_limbs;
-    N->bits = mbedtls_mpi_core_bitlen(p, p_limbs);
-    N->int_rep = MBEDTLS_MPI_MOD_REP_MONTGOMERY;
+    standard_modulus_setup(N, p, p_limbs, MBEDTLS_MPI_MOD_REP_MONTGOMERY);
     N->rep.mont.mm = mbedtls_mpi_core_montmul_init(N->p);
     ret = set_mont_const_square(&N->rep.mont.rr, N->p, N->limbs);
 
@@ -160,10 +168,7 @@ int mbedtls_mpi_mod_optred_modulus_setup(mbedtls_mpi_mod_modulus *N,
                                          size_t p_limbs,
                                          mbedtls_mpi_opt_red_struct *ored)
 {
-    N->p = p;
-    N->limbs = p_limbs;
-    N->bits = mbedtls_mpi_core_bitlen(p, p_limbs);
-    N->int_rep = MBEDTLS_MPI_MOD_REP_OPT_RED;
+    standard_modulus_setup(N, p, p_limbs, MBEDTLS_MPI_MOD_REP_OPT_RED);
     N->rep.ored =ored ;
     return 0;
 }