diff --git a/library/bignum_mod.h b/library/bignum_mod.h
index 432cd00..342bf17 100644
--- a/library/bignum_mod.h
+++ b/library/bignum_mod.h
@@ -67,7 +67,8 @@
 
 int mbedtls_mpi_mod_residue_setup( mbedtls_mpi_mod_residue *r,
                                    mbedtls_mpi_mod_modulus *m,
-                                   mbedtls_mpi_uint *p );
+                                   mbedtls_mpi_uint *p,
+                                   size_t pn );
 
 void mbedtls_mpi_mod_modulus_init( mbedtls_mpi_mod_modulus *m );
 
diff --git a/library/bignum_new.c b/library/bignum_new.c
index 04f6049..60f50ad 100644
--- a/library/bignum_new.c
+++ b/library/bignum_new.c
@@ -29,6 +29,7 @@
 #include "bignum_core.h"
 #include "bignum_mod.h"
 #include "bignum_mod_raw.h"
+#include "constant_time_internal.h"
 
 #if defined(MBEDTLS_PLATFORM_C)
 #include "mbedtls/platform.h"
@@ -92,13 +93,17 @@
 
 int mbedtls_mpi_mod_residue_setup( mbedtls_mpi_mod_residue *r,
                                    mbedtls_mpi_mod_modulus *m,
-                                   mbedtls_mpi_uint *X )
+                                   mbedtls_mpi_uint *p,
+                                   size_t pn )
 {
-    if( X == NULL || m == NULL || r == NULL || X >= m->p)
+    if( p == NULL || m == NULL || r == NULL )
+        return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
+
+    if( pn < m->n || !mbedtls_mpi_core_lt_ct( m->p, p, pn ) )
         return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
 
     r->n = m->n;
-    r->p = X;
+    r->p = p;
 
     return( 0 );
 }
@@ -447,16 +452,28 @@
                               unsigned char *buf,
                               size_t buflen )
 {
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+
     if( m->ext_rep & MBEDTLS_MPI_MOD_EXT_REP_LE )
-        return mbedtls_mpi_core_read_le( X, m->n, buf, buflen );
+        ret = mbedtls_mpi_core_read_le( X, m->n, buf, buflen );
 
     else if( m->ext_rep & MBEDTLS_MPI_MOD_EXT_REP_BE )
-        return mbedtls_mpi_core_read_be( X, m->n, buf, buflen );
-
+        ret = mbedtls_mpi_core_read_be( X, m->n, buf, buflen );
     else
         return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
 
-    return( 0 );
+    if( ret != 0 )
+        goto cleanup;
+
+    if( !mbedtls_mpi_core_lt_ct( X, m->p, m->n ) )
+    {
+        ret = MBEDTLS_ERR_MPI_BAD_INPUT_DATA;
+        goto cleanup;
+    }
+
+cleanup:
+
+    return( ret );
 }
 
 int mbedtls_mpi_mod_raw_write( mbedtls_mpi_uint *X,