diff --git a/library/bignum_core.c b/library/bignum_core.c
index c6d92fb06..26aff15f1 100644
--- a/library/bignum_core.c
+++ b/library/bignum_core.c
@@ -353,6 +353,54 @@ void mbedtls_mpi_core_shift_r(mbedtls_mpi_uint *X, size_t limbs,
     }
 }
 
+int mbedtls_mpi_shift_l( mbedtls_mpi *X, size_t count )
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    size_t i, v0, t1;
+    mbedtls_mpi_uint r0 = 0, r1;
+    MPI_VALIDATE_RET( X != NULL );
+
+    v0 = count / (biL    );
+    t1 = count & (biL - 1);
+
+    i = mbedtls_mpi_bitlen( X ) + count;
+
+    if( X->n * biL < i )
+        MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, BITS_TO_LIMBS( i ) ) );
+
+    ret = 0;
+
+    /*
+     * shift by count / limb_size
+     */
+    if( v0 > 0 )
+    {
+        for( i = X->n; i > v0; i-- )
+            X->p[i - 1] = X->p[i - v0 - 1];
+
+        for( ; i > 0; i-- )
+            X->p[i - 1] = 0;
+    }
+
+    /*
+     * shift by count % limb_size
+     */
+    if( t1 > 0 )
+    {
+        for( i = v0; i < X->n; i++ )
+        {
+            r1 = X->p[i] >> (biL - t1);
+            X->p[i] <<= t1;
+            X->p[i] |= r0;
+            r0 = r1;
+        }
+    }
+
+cleanup:
+
+    return( ret );
+}
+
 mbedtls_mpi_uint mbedtls_mpi_core_add(mbedtls_mpi_uint *X,
                                       const mbedtls_mpi_uint *A,
                                       const mbedtls_mpi_uint *B,
diff --git a/library/bignum_core.h b/library/bignum_core.h
index b3d05a34e..25e7e1a6b 100644
--- a/library/bignum_core.h
+++ b/library/bignum_core.h
@@ -293,6 +293,18 @@ int mbedtls_mpi_core_write_be(const mbedtls_mpi_uint *A,
 void mbedtls_mpi_core_shift_r(mbedtls_mpi_uint *X, size_t limbs,
                               size_t count);
 
+/**
+ * \brief          Perform a left-shift on an MPI: X <<= count
+ *
+ * \param X        The MPI to shift. This must point to an initialized MPI.
+ * \param count    The number of bits to shift by.
+ *
+ * \return         \c 0 if successful.
+ * \return         #MBEDTLS_ERR_MPI_ALLOC_FAILED if a memory allocation failed.
+ * \return         Another negative error code on different kinds of failure.
+ */
+int mbedtls_mpi_shift_l( mbedtls_mpi *X, size_t count );
+
 /**
  * \brief Add two fixed-size large unsigned integers, returning the carry.
  *