diff --git a/library/bignum.c b/library/bignum.c
index 1b80200..7e35aa6 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -862,12 +862,19 @@
 
     if( X == B )
     {
-        const mbedtls_mpi *T;
+        if( B == A )
+        {
+            // Making a temporary copy instead of shifting by one to deny
+            // the possibility of corresponding side-channel attacks.
+            mbedtls_mpi TB;
 
-        if( B == A)
-            return mbedtls_mpi_shift_l( X, 1 );
+            mbedtls_mpi_init( &TB );
+            MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &TB, B ) );
+            
+            return mbedtls_mpi_add_abs( X, A, &TB );
+        }
 
-        T = A; A = X; B = T;
+        B = A; A = X;
     }
 
     if( X != A )
diff --git a/tests/suites/test_suite_mpi.function b/tests/suites/test_suite_mpi.function
index 788893b..2a709bc 100644
--- a/tests/suites/test_suite_mpi.function
+++ b/tests/suites/test_suite_mpi.function
@@ -448,8 +448,17 @@
     mbedtls_mpi X, A;
     mbedtls_mpi_init( &X ); mbedtls_mpi_init( &A );
 
-    TEST_ASSERT( mbedtls_mpi_read_string( &X, radix_X, input_X ) == 0 );
     TEST_ASSERT( mbedtls_mpi_read_string( &A, radix_A, input_A ) == 0 );
+
+    TEST_ASSERT( mbedtls_mpi_read_string( &X, radix_X, input_X ) == 0 );
+    TEST_ASSERT( mbedtls_mpi_sub_abs( &X, &X, &X ) == 0 );
+    TEST_ASSERT( mbedtls_mpi_cmp_int( &X, 0 ) == 0 );
+
+    TEST_ASSERT( mbedtls_mpi_read_string( &X, radix_X, input_X ) == 0 );
+    TEST_ASSERT( mbedtls_mpi_add_abs( &X, &X, &X ) == 0 );
+    TEST_ASSERT( mbedtls_mpi_cmp_mpi( &X, &A ) == 0 );
+
+    TEST_ASSERT( mbedtls_mpi_read_string( &X, radix_X, input_X ) == 0 );
     TEST_ASSERT( mbedtls_mpi_add_mpi( &X, &X, &X ) == 0 );
     TEST_ASSERT( mbedtls_mpi_cmp_mpi( &X, &A ) == 0 );