diff --git a/tf-psa-crypto/tests/suites/test_suite_bignum.function b/tf-psa-crypto/tests/suites/test_suite_bignum.function
index 3d2b8a1..36f1476 100644
--- a/tf-psa-crypto/tests/suites/test_suite_bignum.function
+++ b/tf-psa-crypto/tests/suites/test_suite_bignum.function
@@ -212,28 +212,22 @@
                       int output_size, int result)
 {
     mbedtls_mpi X;
-    unsigned char buf[1000];
-    size_t buflen;
-
-    memset(buf, 0x00, 1000);
-
     mbedtls_mpi_init(&X);
+    unsigned char *buf = NULL;
 
-    TEST_ASSERT(mbedtls_test_read_mpi(&X, input_X) == 0);
+    TEST_EQUAL(mbedtls_test_read_mpi(&X, input_X), 0);
 
-    buflen = mbedtls_mpi_size(&X);
-    if (buflen > (size_t) output_size) {
-        buflen = (size_t) output_size;
-    }
+    TEST_CALLOC(buf, output_size);
 
-    TEST_ASSERT(mbedtls_mpi_write_binary(&X, buf, buflen) == result);
+    TEST_EQUAL(mbedtls_mpi_write_binary(&X, buf, output_size), result);
+
     if (result == 0) {
-
-        TEST_ASSERT(mbedtls_test_hexcmp(buf, input_A->x,
-                                        buflen, input_A->len) == 0);
+        TEST_EQUAL(mbedtls_test_hexcmp(buf, input_A->x,
+                                       output_size, input_A->len), 0);
     }
 
 exit:
+    mbedtls_free(buf);
     mbedtls_mpi_free(&X);
 }
 /* END_CASE */
@@ -243,28 +237,22 @@
                          int output_size, int result)
 {
     mbedtls_mpi X;
-    unsigned char buf[1000];
-    size_t buflen;
-
-    memset(buf, 0x00, 1000);
-
     mbedtls_mpi_init(&X);
+    unsigned char *buf = NULL;
 
-    TEST_ASSERT(mbedtls_test_read_mpi(&X, input_X) == 0);
+    TEST_EQUAL(mbedtls_test_read_mpi(&X, input_X), 0);
 
-    buflen = mbedtls_mpi_size(&X);
-    if (buflen > (size_t) output_size) {
-        buflen = (size_t) output_size;
-    }
+    TEST_CALLOC(buf, output_size);
 
-    TEST_ASSERT(mbedtls_mpi_write_binary_le(&X, buf, buflen) == result);
+    TEST_EQUAL(mbedtls_mpi_write_binary_le(&X, buf, output_size), result);
+
     if (result == 0) {
-
-        TEST_ASSERT(mbedtls_test_hexcmp(buf, input_A->x,
-                                        buflen, input_A->len) == 0);
+        TEST_EQUAL(mbedtls_test_hexcmp(buf, input_A->x,
+                                       output_size, input_A->len), 0);
     }
 
 exit:
+    mbedtls_free(buf);
     mbedtls_mpi_free(&X);
 }
 /* END_CASE */
diff --git a/tf-psa-crypto/tests/suites/test_suite_bignum.misc.data b/tf-psa-crypto/tests/suites/test_suite_bignum.misc.data
index de2ea87..189472f 100644
--- a/tf-psa-crypto/tests/suites/test_suite_bignum.misc.data
+++ b/tf-psa-crypto/tests/suites/test_suite_bignum.misc.data
@@ -92,7 +92,7 @@
 mpi_read_binary_le:"0941379d00fed1491fe15df284dfde4a142f68aa8d412023195cee66883e6290ffe703f4ea5963bf212713cee46b107c09182b5edcd955adac418bf4918e2889af48e1099d513830cec85c26ac1e158b52620e33ba8692f893efbb2f958b4424":"24448B952FBBEF93F89286BA330E62528B151EAC265CC8CE3038519D09E148AF89288E91F48B41ACAD55D9DC5E2B18097C106BE4CE132721BF6359EAF403E7FF90623E8866EE5C192320418DAA682F144ADEDF84F25DE11F49D1FE009D374109"
 
 Base test mbedtls_mpi_write_binary #1
-mpi_write_binary:"941379d00fed1491fe15df284dfde4a142f68aa8d412023195cee66883e6290ffe703f4ea5963bf212713cee46b107c09182b5edcd955adac418bf4918e2889af48e1099d513830cec85c26ac1e158b52620e33ba8692f893efbb2f958b4424":"0941379d00fed1491fe15df284dfde4a142f68aa8d412023195cee66883e6290ffe703f4ea5963bf212713cee46b107c09182b5edcd955adac418bf4918e2889af48e1099d513830cec85c26ac1e158b52620e33ba8692f893efbb2f958b4424":200:0
+mpi_write_binary:"941379d00fed1491fe15df284dfde4a142f68aa8d412023195cee66883e6290ffe703f4ea5963bf212713cee46b107c09182b5edcd955adac418bf4918e2889af48e1099d513830cec85c26ac1e158b52620e33ba8692f893efbb2f958b4424":"000000000941379d00fed1491fe15df284dfde4a142f68aa8d412023195cee66883e6290ffe703f4ea5963bf212713cee46b107c09182b5edcd955adac418bf4918e2889af48e1099d513830cec85c26ac1e158b52620e33ba8692f893efbb2f958b4424":100:0
 
 Test mbedtls_mpi_write_binary #1 (Buffer just fits)
 mpi_write_binary:"123123123123123123123123123":"0123123123123123123123123123":14:0
@@ -101,7 +101,7 @@
 mpi_write_binary:"123123123123123123123123123":"23123123123123123123123123":13:MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL
 
 Base test mbedtls_mpi_write_binary_le #1
-mpi_write_binary_le:"941379d00fed1491fe15df284dfde4a142f68aa8d412023195cee66883e6290ffe703f4ea5963bf212713cee46b107c09182b5edcd955adac418bf4918e2889af48e1099d513830cec85c26ac1e158b52620e33ba8692f893efbb2f958b4424":"24448b952fbbef93f89286ba330e62528b151eac265cc8ce3038519d09e148af89288e91f48b41acad55d9dc5e2b18097c106be4ce132721bf6359eaf403e7ff90623e8866ee5c192320418daa682f144adedf84f25de11f49d1fe009d374109":200:0
+mpi_write_binary_le:"941379d00fed1491fe15df284dfde4a142f68aa8d412023195cee66883e6290ffe703f4ea5963bf212713cee46b107c09182b5edcd955adac418bf4918e2889af48e1099d513830cec85c26ac1e158b52620e33ba8692f893efbb2f958b4424":"24448b952fbbef93f89286ba330e62528b151eac265cc8ce3038519d09e148af89288e91f48b41acad55d9dc5e2b18097c106be4ce132721bf6359eaf403e7ff90623e8866ee5c192320418daa682f144adedf84f25de11f49d1fe009d37410900000000":100:0
 
 Test mbedtls_mpi_write_binary_le #1 (Buffer just fits)
 mpi_write_binary_le:"123123123123123123123123123":"2331122331122331122331122301":14:0