diff --git a/library/bignum_core.c b/library/bignum_core.c
index 6aa1e00066..9adc4effb0 100644
--- a/library/bignum_core.c
+++ b/library/bignum_core.c
@@ -162,59 +162,36 @@ void mbedtls_mpi_core_bigendian_to_host( mbedtls_mpi_uint *A,
     }
 }
 
-int mbedtls_mpi_core_cond_assign( mbedtls_mpi_uint *X,
-                                  size_t X_limbs,
-                                  const mbedtls_mpi_uint *Y,
-                                  size_t Y_limbs,
-                                  unsigned char assign )
+void mbedtls_mpi_core_cond_assign( mbedtls_mpi_uint *X,
+                                   size_t X_limbs,
+                                   const mbedtls_mpi_uint *Y,
+                                   size_t Y_limbs,
+                                   unsigned char assign )
 {
-    if( X_limbs < Y_limbs )
-        return( MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL );
+    /* all-bits 1 if assign is 1, all-bits 0 if assign is 0 */
+    mbedtls_mpi_uint limb_mask = mbedtls_ct_mpi_uint_mask( assign );
 
-    if( X != NULL && Y != NULL )
-    {
-        /* all-bits 1 if assign is 1, all-bits 0 if assign is 0 */
-        mbedtls_mpi_uint limb_mask = mbedtls_ct_mpi_uint_mask( assign );
+    mbedtls_ct_mpi_uint_cond_assign( Y_limbs, X, Y, assign );
 
-        mbedtls_ct_mpi_uint_cond_assign( X_limbs, X, Y, assign );
-
-        for( size_t i = Y_limbs; i < X_limbs; i++ )
-            X[i] &= ~limb_mask;
-
-        return( 0 );
-    }
-
-    return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
+    for( size_t i = Y_limbs; i < X_limbs; i++ )
+        X[i] &= ~limb_mask;
 }
 
-int mbedtls_mpi_core_cond_swap( mbedtls_mpi_uint *X,
-                                size_t X_limbs,
-                                mbedtls_mpi_uint *Y,
-                                size_t Y_limbs,
-                                unsigned char swap )
+void mbedtls_mpi_core_cond_swap( mbedtls_mpi_uint *X,
+                                 size_t X_limbs,
+                                 mbedtls_mpi_uint *Y,
+                                 size_t Y_limbs,
+                                 unsigned char swap )
 {
-    if( X == Y )
-        return( 0 );
+    /* all-bits 1 if swap is 1, all-bits 0 if swap is 0 */
+    mbedtls_mpi_uint limb_mask = mbedtls_ct_mpi_uint_mask( swap );
 
-    if( X_limbs != Y_limbs )
-        return( MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL );
-
-    if( X != NULL && Y != NULL )
+    for( size_t i = 0; i < X_limbs; i++ )
     {
-        /* all-bits 1 if swap is 1, all-bits 0 if swap is 0 */
-        mbedtls_mpi_uint limb_mask = mbedtls_ct_mpi_uint_mask( swap );
-
-        for( size_t i = 0; i < X_limbs; i++ )
-        {
-            mbedtls_mpi_uint tmp = X[i];
-            X[i] = ( X[i] & ~limb_mask ) | ( Y[i] & limb_mask );
-            Y[i] = ( Y[i] & ~limb_mask ) | (  tmp & limb_mask );
-        }
-
-        return( 0 );
+        mbedtls_mpi_uint tmp = X[i];
+        X[i] = ( X[i] & ~limb_mask ) | ( Y[i] & limb_mask );
+        Y[i] = ( Y[i] & ~limb_mask ) | (  tmp & limb_mask );
     }
-
-    return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
 }
 
 int mbedtls_mpi_core_read_le( mbedtls_mpi_uint *X,
diff --git a/library/bignum_core.h b/library/bignum_core.h
index 24650fe4c8..a538ece0f5 100644
--- a/library/bignum_core.h
+++ b/library/bignum_core.h
@@ -93,17 +93,12 @@ void mbedtls_mpi_core_bigendian_to_host( mbedtls_mpi_uint *A,
  * \warning        If \p assign is neither 0 nor 1, the result of this function
  *                 is indeterminate, and the resulting value in \p X might be
  *                 neither its original value nor the value in \p Y.
- *
- * \return         \c 0 if successful.
- * \return         #MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL if \p X isn't
- *                 large enough to hold the value in \p Y.
- * \return         #MBEDTLS_ERR_MPI_BAD_INPUT_DATA if \p X or \p Y is invalid.
  */
-int mbedtls_mpi_core_cond_assign( mbedtls_mpi_uint *X,
-                                  size_t X_limbs,
-                                  const mbedtls_mpi_uint *Y,
-                                  size_t Y_limbs,
-                                  unsigned char assign );
+void mbedtls_mpi_core_cond_assign( mbedtls_mpi_uint *X,
+                                   size_t X_limbs,
+                                   const mbedtls_mpi_uint *Y,
+                                   size_t Y_limbs,
+                                   unsigned char assign );
 
 /**
  * \brief   Perform a safe conditional copy of MPI which doesn't reveal whether
@@ -126,17 +121,12 @@ int mbedtls_mpi_core_cond_assign( mbedtls_mpi_uint *X,
  * \warning        If \p swap is neither 0 nor 1, the result of this function
  *                 is indeterminate, and both \p X and \p Y might end up with
  *                 values different to either of the original ones.
- *
- * \return         \c 0 if successful.
- * \return         #MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL if the size of
- *                 \p X and \p Y is differ.
- * \return         #MBEDTLS_ERR_MPI_BAD_INPUT_DATA if \p X or \p Y is invalid.
  */
-int mbedtls_mpi_core_cond_swap( mbedtls_mpi_uint *X,
-                                size_t X_limbs,
-                                mbedtls_mpi_uint *Y,
-                                size_t Y_limbs,
-                                unsigned char swap );
+void mbedtls_mpi_core_cond_swap( mbedtls_mpi_uint *X,
+                                 size_t X_limbs,
+                                 mbedtls_mpi_uint *Y,
+                                 size_t Y_limbs,
+                                 unsigned char swap );
 
 /** Import X from unsigned binary data, little-endian.
  *