diff --git a/tests/suites/test_suite_pk.function b/tests/suites/test_suite_pk.function
index c0c987d5c..bb3eceead 100644
--- a/tests/suites/test_suite_pk.function
+++ b/tests/suites/test_suite_pk.function
@@ -125,18 +125,18 @@ void pk_rsa_verify_test_vec( char *message_hex_string, int digest,
                        int mod, int radix_N, char *input_N, int radix_E,
                        char *input_E, char *result_hex_str, int result )
 {
-    unsigned char message_str[1000];
-    unsigned char hash_result[1000];
-    unsigned char result_str[1000];
+    unsigned char message_str[128];
+    unsigned char hash_result[MBEDTLS_MD_MAX_SIZE];
+    unsigned char result_str[128];
     mbedtls_rsa_context *rsa;
     mbedtls_pk_context pk;
     int msg_len;
 
     mbedtls_pk_init( &pk );
 
-    memset( message_str, 0x00, 1000 );
-    memset( hash_result, 0x00, 1000 );
-    memset( result_str, 0x00, 1000 );
+    memset( message_str, 0x00, sizeof( message_str ) );
+    memset( hash_result, 0x00, sizeof( hash_result ) );
+    memset( result_str, 0x00, sizeof(result_str ) );
 
     TEST_ASSERT( mbedtls_pk_setup( &pk, mbedtls_pk_info_from_type( MBEDTLS_PK_RSA ) ) == 0 );
     rsa = mbedtls_pk_rsa( pk );
@@ -166,9 +166,9 @@ void pk_rsa_verify_ext_test_vec( char *message_hex_string, int digest,
                        int pk_type, int mgf1_hash_id, int salt_len,
                        int result )
 {
-    unsigned char message_str[1000];
-    unsigned char hash_result[1000];
-    unsigned char result_str[1000];
+    unsigned char message_str[128];
+    unsigned char hash_result[MBEDTLS_MD_MAX_SIZE];
+    unsigned char result_str[128];
     mbedtls_rsa_context *rsa;
     mbedtls_pk_context pk;
     mbedtls_pk_rsassa_pss_options pss_opts;
@@ -178,9 +178,9 @@ void pk_rsa_verify_ext_test_vec( char *message_hex_string, int digest,
 
     mbedtls_pk_init( &pk );
 
-    memset( message_str, 0x00, 1000 );
-    memset( hash_result, 0x00, 1000 );
-    memset( result_str, 0x00, 1000 );
+    memset( message_str, 0x00, sizeof( message_str ) );
+    memset( hash_result, 0x00, sizeof( hash_result ) );
+    memset( result_str, 0x00, sizeof( result_str ) );
 
     TEST_ASSERT( mbedtls_pk_setup( &pk, mbedtls_pk_info_from_type( MBEDTLS_PK_RSA ) ) == 0 );
     rsa = mbedtls_pk_rsa( pk );
@@ -289,9 +289,9 @@ void pk_rsa_encrypt_test_vec( char *message_hex, int mod,
                             int radix_E, char *input_E,
                             char *result_hex, int ret )
 {
-    unsigned char message[1000];
-    unsigned char output[1000];
-    unsigned char result[1000];
+    unsigned char message[16];
+    unsigned char output[300];
+    unsigned char result[256];
     size_t msg_len, olen, res_len;
     rnd_pseudo_info rnd_info;
     mbedtls_rsa_context *rsa;
@@ -332,9 +332,9 @@ void pk_rsa_decrypt_test_vec( char *cipher_hex, int mod,
                             int radix_E, char *input_E,
                             char *clear_hex, int ret )
 {
-    unsigned char clear[1000];
-    unsigned char output[1000];
-    unsigned char cipher[1000];
+    unsigned char clear[16];
+    unsigned char output[256];
+    unsigned char cipher[256];
     size_t clear_len, olen, cipher_len;
     rnd_pseudo_info rnd_info;
     mbedtls_mpi N, P, Q, E;
@@ -463,8 +463,8 @@ void pk_rsa_alt( )
     mbedtls_rsa_context raw;
     mbedtls_pk_context rsa, alt;
     mbedtls_pk_debug_item dbg_items[10];
-    unsigned char hash[50], sig[1000];
-    unsigned char msg[50], ciph[1000], test[1000];
+    unsigned char hash[50], sig[64];
+    unsigned char msg[50], ciph[64], test[50];
     size_t sig_len, ciph_len, test_len;
     int ret = MBEDTLS_ERR_PK_TYPE_MISMATCH;