diff --git a/tests/suites/test_suite_ecp.function b/tests/suites/test_suite_ecp.function
index e5dddc4..d22be43 100644
--- a/tests/suites/test_suite_ecp.function
+++ b/tests/suites/test_suite_ecp.function
@@ -1596,7 +1596,6 @@
     memset(A, 0, limbs * ciL);
     ASSERT_COMPARE(&bufx[1], (limbs - 1) * ciL, A, (limbs - 1) * ciL);
 
-
 exit:
     mbedtls_mpi_mod_modulus_free(&m);
     mbedtls_mpi_mod_residue_release(&rA);
@@ -1608,3 +1607,63 @@
     mbedtls_free(bufx);
 }
 /* END_CASE */
+
+/* BEGIN_CASE depends_on:MBEDTLS_TEST_HOOKS */
+void ecp_mod_add_sub(char *input_A, char *input_B, int id, int ctype, int iret)
+{
+    int ret;
+    mbedtls_mpi_mod_modulus m;
+    mbedtls_mpi_mod_modulus_init(&m);
+    mbedtls_mpi_uint *p_A = NULL;
+    mbedtls_mpi_uint *p_B = NULL;
+    mbedtls_mpi_uint *p_S = NULL;
+    mbedtls_mpi_mod_residue rA = { NULL, 0 };
+    mbedtls_mpi_mod_residue rB = { NULL, 0 };
+    mbedtls_mpi_mod_residue rS = { NULL, 0 };
+    size_t p_limbs;
+    size_t bytes;
+
+    TEST_EQUAL(mbedtls_test_read_mpi_core(&p_A, &p_limbs, input_A), 0);
+
+    ret = mbedtls_ecp_modulus_setup(&m, id, ctype);
+    TEST_EQUAL(ret, iret);
+
+    if (ret == 0) {
+
+        /* Test for limb sizes */
+        TEST_EQUAL(m.limbs, p_limbs);
+        bytes = p_limbs * sizeof(mbedtls_mpi_uint);
+
+        /* Test for validity of moduli by the presence of Montgomery consts */
+
+        TEST_ASSERT(m.rep.mont.mm != 0);
+        TEST_ASSERT(m.rep.mont.rr != NULL);
+
+        ASSERT_ALLOC(p_S, p_limbs);
+
+        TEST_EQUAL(mbedtls_test_read_mpi_core(&p_B, &p_limbs, input_B), 0);
+        TEST_EQUAL(mbedtls_mpi_mod_residue_setup(&rA, &m, p_A, p_limbs), 0);
+        TEST_EQUAL(mbedtls_mpi_mod_residue_setup(&rB, &m, p_B, p_limbs), 0);
+        TEST_EQUAL(mbedtls_mpi_mod_residue_setup(&rS, &m, p_S, p_limbs), 0);
+
+        TEST_EQUAL(0, mbedtls_mpi_mod_add(&rS, &rA, &rB, &m));
+        TEST_EQUAL(0, mbedtls_mpi_mod_sub(&rS, &rS, &rB, &m));
+
+
+        /* Compare output byte-by-byte */
+        ASSERT_COMPARE(rA.p, bytes, rS.p, bytes);
+
+        /* Test for user free-ing allocated memory */
+        mbedtls_mpi_mod_modulus_free(&m);
+    }
+
+exit:
+    mbedtls_mpi_mod_modulus_free(&m);
+    mbedtls_mpi_mod_residue_release(&rA);
+    mbedtls_mpi_mod_residue_release(&rB);
+    mbedtls_mpi_mod_residue_release(&rS);
+    mbedtls_free(p_A);
+    mbedtls_free(p_B);
+    mbedtls_free(p_S);
+}
+/* END_CASE */