diff --git a/tests/suites/test_suite_asn1write.data b/tests/suites/test_suite_asn1write.data
index 0c4074e..3518ed9 100644
--- a/tests/suites/test_suite_asn1write.data
+++ b/tests/suites/test_suite_asn1write.data
@@ -50,22 +50,31 @@
 mbedtls_asn1_write_ia5_string:"ABC":"":2:MBEDTLS_ERR_ASN1_BUF_TOO_SMALL
 
 ASN.1 Write / Read Length #0 (Len = 0, short form)
-mbedtls_asn1_write_len:0:"00":1
+mbedtls_asn1_write_len:0:"00":1:1
 
 ASN.1 Write / Read Length #1 (Len = 127, short form)
-mbedtls_asn1_write_len:127:"7F":1
+mbedtls_asn1_write_len:127:"7F":1:1
 
-ASN.1 Write / Read Length #2 (Len = 128, long form)
-mbedtls_asn1_write_len:128:"8180":2
+ASN.1 Write / Read Length #2 (Len = 127, buffer too small)
+mbedtls_asn1_write_len:127:"7F":0:MBEDTLS_ERR_ASN1_BUF_TOO_SMALL
 
-ASN.1 Write / Read Length #3 (Len = 255, long form)
-mbedtls_asn1_write_len:255:"81FF":2
+ASN.1 Write / Read Length #3 (Len = 128, long form)
+mbedtls_asn1_write_len:128:"8180":2:2
 
-ASN.1 Write / Read Length #4 (Len = 256, long form)
-mbedtls_asn1_write_len:256:"820100":3
+ASN.1 Write / Read Length #4 (Len = 255, long form)
+mbedtls_asn1_write_len:255:"81FF":2:2
 
-ASN.1 Write / Read Length #5 (Len = 65535, max supported length)
-mbedtls_asn1_write_len:65535:"82FFFF":3
+ASN.1 Write / Read Length #5 (Len = 255, buffer too small)
+mbedtls_asn1_write_len:255:"81FF":1:MBEDTLS_ERR_ASN1_BUF_TOO_SMALL
 
-ASN.1 Write / Read Length #6 (Len = 65536, not supported)
-mbedtls_asn1_write_len:65536:"":MBEDTLS_ERR_ASN1_INVALID_LENGTH
+ASN.1 Write / Read Length #6 (Len = 256, long form)
+mbedtls_asn1_write_len:256:"820100":3:3
+
+ASN.1 Write / Read Length #7 (Len = 65535, max supported length)
+mbedtls_asn1_write_len:65535:"82FFFF":3:3
+
+ASN.1 Write / Read Length #8 (Len = 65535, buffer too small)
+mbedtls_asn1_write_len:65535:"82FFFF":2:MBEDTLS_ERR_ASN1_BUF_TOO_SMALL
+
+ASN.1 Write / Read Length #9 (Len = 65536, not supported)
+mbedtls_asn1_write_len:65536:"":0:MBEDTLS_ERR_ASN1_INVALID_LENGTH
diff --git a/tests/suites/test_suite_asn1write.function b/tests/suites/test_suite_asn1write.function
index 160190f..ba4db88 100644
--- a/tests/suites/test_suite_asn1write.function
+++ b/tests/suites/test_suite_asn1write.function
@@ -84,7 +84,8 @@
 /* END_CASE */
 
 /* BEGIN_CASE */
-void mbedtls_asn1_write_len( int len, char *check_str, int result )
+void mbedtls_asn1_write_len( int len, char *check_str, int buf_len,
+                             int result )
 {
     int ret;
     unsigned char buf[150];
@@ -96,7 +97,7 @@
     memset( asn1, 0, sizeof( asn1 ) );
     asn1_len = unhexify( asn1, check_str );
 
-    p = buf + GUARD_LEN + asn1_len;
+    p = buf + GUARD_LEN + buf_len;
 
     ret = mbedtls_asn1_write_len( &p, buf + GUARD_LEN, (size_t) len );
 
@@ -106,13 +107,13 @@
     for( i = 0; i < GUARD_LEN; i++ )
     {
         TEST_ASSERT( buf[i] == GUARD_VAL );
-        TEST_ASSERT( buf[GUARD_LEN + asn1_len + i] == GUARD_VAL );
+        TEST_ASSERT( buf[GUARD_LEN + buf_len + i] == GUARD_VAL );
     }
 
     if( result >= 0 )
     {
         TEST_ASSERT( (size_t) ret == asn1_len );
-        TEST_ASSERT( p + asn1_len == buf + GUARD_LEN + asn1_len );
+        TEST_ASSERT( p + asn1_len == buf + GUARD_LEN + buf_len );
 
         TEST_ASSERT( memcmp( p, asn1, asn1_len ) == 0 );
     }