diff --git a/tests/suites/test_suite_chacha20.function b/tests/suites/test_suite_chacha20.function
index 75d2d0fc9..9c0b98522 100644
--- a/tests/suites/test_suite_chacha20.function
+++ b/tests/suites/test_suite_chacha20.function
@@ -14,21 +14,21 @@ void chacha20_crypt( char *hex_key_string,
                      char *hex_src_string,
                      char *hex_dst_string )
 {
-    unsigned char key_str[100];
-    unsigned char nonce_str[100];
-    unsigned char src_str[10000];
-    unsigned char dst_str[10000];
-    unsigned char output[10000];
+    unsigned char key_str[32]; /* size set by the standard */
+    unsigned char nonce_str[12]; /* size set by the standard */
+    unsigned char src_str[375]; /* max size of binary input */
+    unsigned char dst_str[751]; /* hex expansion of the above */
+    unsigned char output[751];
     size_t key_len;
     size_t nonce_len;
     size_t src_len;
     size_t dst_len;
 
-    memset(key_str, 0x00, 100);
-    memset(nonce_str, 0x00, 100);
-    memset(src_str, 0x00, 10000);
-    memset(dst_str, 0x00, 10000);
-    memset(output, 0x00, 10000);
+    memset( key_str,    0x00, sizeof( key_str ) );
+    memset( nonce_str,  0x00, sizeof( nonce_str ) );
+    memset( src_str,    0x00, sizeof( src_str ) );
+    memset( dst_str,    0x00, sizeof( dst_str ) );
+    memset( output,     0x00, sizeof( output ) );
 
     key_len   = unhexify( key_str, hex_key_string );
     nonce_len = unhexify( nonce_str, hex_nonce_string );
@@ -52,4 +52,4 @@ void chacha20_self_test()
 {
     TEST_ASSERT( mbedtls_chacha20_self_test( 0 ) == 0 );
 }
-/* END_CASE */
\ No newline at end of file
+/* END_CASE */
diff --git a/tests/suites/test_suite_chachapoly.function b/tests/suites/test_suite_chachapoly.function
index b205c4ce0..3d6a2b6d1 100644
--- a/tests/suites/test_suite_chachapoly.function
+++ b/tests/suites/test_suite_chachapoly.function
@@ -10,14 +10,14 @@
 /* BEGIN_CASE */
 void mbedtls_chachapoly_enc( char *hex_key_string, char *hex_nonce_string, char *hex_aad_string, char *hex_input_string, char *hex_output_string, char *hex_mac_string )
 {
-    unsigned char key_str[32];
-    unsigned char nonce_str[12];
-    unsigned char aad_str[10000];
-    unsigned char input_str[10000];
-    unsigned char output_str[10000];
-    unsigned char mac_str[16];
-    unsigned char output[10000];
-    unsigned char mac[16];
+    unsigned char key_str[32]; /* size set by the standard */
+    unsigned char nonce_str[12]; /* size set by the standard */
+    unsigned char aad_str[12]; /* max size of test data so far */
+    unsigned char input_str[265]; /* max size of binary input/output so far */
+    unsigned char output_str[265];
+    unsigned char output[265];
+    unsigned char mac_str[16]; /* size set by the standard */
+    unsigned char mac[16]; /* size set by the standard */
     size_t input_len;
     size_t output_len;
     size_t aad_len;
@@ -26,12 +26,12 @@ void mbedtls_chachapoly_enc( char *hex_key_string, char *hex_nonce_string, char
     size_t mac_len;
     mbedtls_chachapoly_context ctx;
 
-    memset( key_str,     0x00, 32    );
-    memset( nonce_str,   0x00, 12    );
-    memset( aad_str,     0x00, 10000 );
-    memset( input_str,   0x00, 10000 );
-    memset( output_str,  0x00, 10000 );
-    memset( mac_str,     0x00, 16    );
+    memset( key_str,    0x00, sizeof( key_str ) );
+    memset( nonce_str,  0x00, sizeof( nonce_str ) );
+    memset( aad_str,    0x00, sizeof( aad_str ) );
+    memset( input_str,  0x00, sizeof( input_str ) );
+    memset( output_str, 0x00, sizeof( output_str ) );
+    memset( mac_str,    0x00, sizeof( mac_str ) );
 
     aad_len    = unhexify( aad_str,    hex_aad_string    );
     input_len  = unhexify( input_str,  hex_input_string  );
@@ -65,13 +65,13 @@ exit:
 /* BEGIN_CASE */
 void mbedtls_chachapoly_dec( char *hex_key_string, char *hex_nonce_string, char *hex_aad_string, char *hex_input_string, char *hex_output_string, char *hex_mac_string )
 {
-    unsigned char key_str[32];
-    unsigned char nonce_str[12];
-    unsigned char aad_str[10000];
-    unsigned char input_str[10000];
-    unsigned char output_str[10000];
-    unsigned char mac_str[16];
-    unsigned char output[10000];
+    unsigned char key_str[32]; /* size set by the standard */
+    unsigned char nonce_str[12]; /* size set by the standard */
+    unsigned char aad_str[12]; /* max size of test data so far */
+    unsigned char input_str[265]; /* max size of binary input/output so far */
+    unsigned char output_str[265];
+    unsigned char output[265];
+    unsigned char mac_str[16]; /* size set by the standard */
     size_t input_len;
     size_t output_len;
     size_t aad_len;
@@ -81,12 +81,12 @@ void mbedtls_chachapoly_dec( char *hex_key_string, char *hex_nonce_string, char
     int ret;
     mbedtls_chachapoly_context ctx;
 
-    memset( key_str,     0x00, 32    );
-    memset( nonce_str,   0x00, 12    );
-    memset( aad_str,     0x00, 10000 );
-    memset( input_str,   0x00, 10000 );
-    memset( output_str,  0x00, 10000 );
-    memset( mac_str,     0x00, 16    );
+    memset( key_str,    0x00, sizeof( key_str ) );
+    memset( nonce_str,  0x00, sizeof( nonce_str ) );
+    memset( aad_str,    0x00, sizeof( aad_str ) );
+    memset( input_str,  0x00, sizeof( input_str ) );
+    memset( output_str, 0x00, sizeof( output_str ) );
+    memset( mac_str,    0x00, sizeof( mac_str ) );
 
     aad_len    = unhexify( aad_str,    hex_aad_string    );
     input_len  = unhexify( input_str,  hex_input_string  );
diff --git a/tests/suites/test_suite_poly1305.function b/tests/suites/test_suite_poly1305.function
index a633c2baa..5ede635c9 100644
--- a/tests/suites/test_suite_poly1305.function
+++ b/tests/suites/test_suite_poly1305.function
@@ -6,16 +6,16 @@
 /* BEGIN_CASE depends_on:MBEDTLS_POLY1305_C */
 void mbedtls_poly1305( char *hex_key_string, char *hex_mac_string, char *hex_src_string  )
 {
-    unsigned char src_str[10000];
-    unsigned char mac_str[100];
-    unsigned char key[32];
-    unsigned char mac[16];
+    unsigned char src_str[375]; /* max size of binary input */
+    unsigned char key[32]; /* size set by the standard */
+    unsigned char mac[16]; /* size set by the standard */
+    unsigned char mac_str[33]; /* hex expansion of the above */
     size_t src_len;
 
-    memset(src_str, 0x00, 10000);
-    memset(mac_str, 0x00, 100);
-    memset(key,     0x00, 32);
-    memset(mac,     0x00, 16);
+    memset( src_str, 0x00, sizeof( src_str ) );
+    memset( mac_str, 0x00, sizeof( mac_str ) );
+    memset( key,     0x00, sizeof( key ) );
+    memset( mac,     0x00, sizeof( mac ) );
 
     src_len = unhexify( src_str, hex_src_string );
     unhexify( key, hex_key_string );