diff --git a/tests/suites/test_suite_bignum.function b/tests/suites/test_suite_bignum.function
index 4cec0a7..e94681a 100644
--- a/tests/suites/test_suite_bignum.function
+++ b/tests/suites/test_suite_bignum.function
@@ -1,8 +1,10 @@
 /* BEGIN_HEADER */
 #include "mbedtls/bignum.h"
+#include "bignum_core.h"
 #include "mbedtls/entropy.h"
 #include "constant_time_internal.h"
 #include "test/constant_flow.h"
+#include "mbedtls/error.h"
 
 #if MBEDTLS_MPI_MAX_BITS > 792
 #define MPI_MAX_BITS_LARGER_THAN_792
@@ -1414,6 +1416,82 @@
 }
 /* END_CASE */
 
+/* BEGIN_CASE */
+void mpi_get_montgomery_constant_unsafe_neg(  )
+{
+    mbedtls_mpi N, RR;
+    mbedtls_mpi_init( &N );
+    mbedtls_mpi_init( &RR );
+    const char * n = "7ffffffffffffff1";
+
+    /* Test for NULL input pointers */
+    TEST_EQUAL( MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED,
+               mbedtls_mpi_get_montgomery_constant_unsafe( NULL, &N ) );
+
+    TEST_EQUAL( MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED,
+               mbedtls_mpi_get_montgomery_constant_unsafe( &RR, NULL ) );
+
+    /* Test for zero divisor */
+    TEST_EQUAL( MBEDTLS_ERR_MPI_DIVISION_BY_ZERO,
+               mbedtls_mpi_get_montgomery_constant_unsafe( &RR, &N ) );
+
+    /* Test for negative input */
+    TEST_EQUAL( 0, mbedtls_test_read_mpi( &N, n ) );
+    N.s = -1;
+    TEST_EQUAL( MBEDTLS_ERR_MPI_NEGATIVE_VALUE,
+               mbedtls_mpi_get_montgomery_constant_unsafe( &RR, &N ) );
+    N.s = 1;
+
+exit:
+    mbedtls_mpi_free( &N );
+    mbedtls_mpi_free( &RR );
+}
+/* END_CASE */
+
+/* BEGIN_CASE */
+void mpi_get_montgomery_constant_unsafe( char * input_N,
+                                         char * input_RR_X4,
+                                         char * input_RR_X8 )
+{
+    mbedtls_mpi N, RR, RR_REF;
+
+    /* Select the appropriate output */
+    char * input_rr = ( sizeof(mbedtls_mpi_uint) == 4 ) ? input_RR_X4: input_RR_X8;
+
+    mbedtls_mpi_init( &N );
+    mbedtls_mpi_init( &RR );
+    mbedtls_mpi_init( &RR_REF );
+
+    /* Read inputs */
+    TEST_EQUAL( 0, mbedtls_test_read_mpi( &N, input_N ) );
+    TEST_EQUAL( 0, mbedtls_test_read_mpi( &RR_REF, input_rr ) );
+
+    /* All of the inputs are +ve (or zero) */
+    TEST_EQUAL( 1, sign_is_valid(&N));
+    TEST_EQUAL( 1, sign_is_valid(&RR_REF));
+
+    /* Test valid input */
+    TEST_EQUAL( 0, mbedtls_mpi_get_montgomery_constant_unsafe( &RR, &N ) );
+
+    /* Test that the moduli is odd */
+    TEST_EQUAL(N.p[0] ^ 1, N.p[0] - 1);
+
+   /* Output is +ve (or zero) */
+    TEST_EQUAL( 1, sign_is_valid(&RR));
+
+    /* rr is updated to a valid pointer */
+    TEST_ASSERT( RR.p != NULL );
+
+    /* Calculated rr matches expected value */
+    TEST_ASSERT( mbedtls_mpi_cmp_mpi( &RR, &RR_REF ) == 0 );
+
+exit:
+    mbedtls_mpi_free( &N );
+    mbedtls_mpi_free( &RR );
+    mbedtls_mpi_free( &RR_REF );
+}
+/* END_CASE */
+
 /* BEGIN_CASE depends_on:MBEDTLS_SELF_TEST */
 void mpi_selftest(  )
 {
diff --git a/tests/suites/test_suite_bignum.misc.data b/tests/suites/test_suite_bignum.misc.data
index 78afcb6..b93b183 100644
--- a/tests/suites/test_suite_bignum.misc.data
+++ b/tests/suites/test_suite_bignum.misc.data
@@ -1902,6 +1902,39 @@
 MPI random bad arguments: min > N = 1, 0 limb in upper bound
 mpi_random_fail:2:"000000000000000001":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
 
+mbedtls_mpi_get_montgomery_constant_unsafe_neg
+mpi_get_montgomery_constant_unsafe_neg:
+
+mbedtls_mpi_get_montgomery_constant_unsafe #1
+mpi_get_montgomery_constant_unsafe:"f":"1":"1"
+
+mbedtls_mpi_get_montgomery_constant_unsafe #2
+mpi_get_montgomery_constant_unsafe:"fd":"ec":"24"
+
+mbedtls_mpi_get_montgomery_constant_unsafe #3
+mpi_get_montgomery_constant_unsafe:"eeff99aa37":"a23bd6a686":"a23bd6a686"
+
+mbedtls_mpi_get_montgomery_constant_unsafe #4
+mpi_get_montgomery_constant_unsafe:"eeff99aa11":"3308cb71":"3308cb71"
+
+mbedtls_mpi_get_montgomery_constant_unsafe #5
+mpi_get_montgomery_constant_unsafe:"800000000005":"6400000000":"6400000000"
+
+mbedtls_mpi_get_montgomery_constant_unsafe #6
+mpi_get_montgomery_constant_unsafe:"7fffffffffffffff":"4":"4"
+
+mbedtls_mpi_get_montgomery_constant_unsafe #7
+mpi_get_montgomery_constant_unsafe:"80fe000a10000001":"5dbc6e833bad575a":"5dbc6e833bad575a"
+
+mbedtls_mpi_get_montgomery_constant_unsafe #8
+mpi_get_montgomery_constant_unsafe:"25a55a46e5da99c71c7":"11637ce1347edeaf669":"1e455bf7451c05bc711"
+
+mbedtls_mpi_get_montgomery_constant_unsafe #9
+mpi_get_montgomery_constant_unsafe:"314dc643fb763f2b8c0e2de00879":"1058ad82120c3a10196bb36229c1":"1058ad82120c3a10196bb36229c1"
+
+mbedtls_mpi_get_montgomery_constant_unsafe #10
+mpi_get_montgomery_constant_unsafe:"8335616aed761f1f7f44e6bd49e807b82e3bf2bf11bfa6af813c808dbf33dbfa11dabd6e6144bef37c6800000000000000000000000000000000051":"78a9f16233856e722242e964006ed8666bfe8e55ea736ea86ce7aa71511e36d9ea1509ad5d821f7777e4a2d885924d15cc11e2ccd85eba69ab04989":"5c9d20a5636b6d7abdec003c1ad87e7c88ebf7238a5d85800d3bc214512cd6269558728307ae94eb389e2ccd85eba69ab0493e8277211ce1be22db"
+
 MPI Selftest
 depends_on:MBEDTLS_SELF_TEST
 mpi_selftest: