diff --git a/tests/suites/test_suite_asn1write.data b/tests/suites/test_suite_asn1write.data
index 61934f5..0c4074e 100644
--- a/tests/suites/test_suite_asn1write.data
+++ b/tests/suites/test_suite_asn1write.data
@@ -48,3 +48,24 @@
 
 ASN.1 Write IA5 String #5 (Buffer too small for string)
 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
+
+ASN.1 Write / Read Length #1 (Len = 127, short form)
+mbedtls_asn1_write_len:127:"7F":1
+
+ASN.1 Write / Read Length #2 (Len = 128, long form)
+mbedtls_asn1_write_len:128:"8180":2
+
+ASN.1 Write / Read Length #3 (Len = 255, long form)
+mbedtls_asn1_write_len:255:"81FF":2
+
+ASN.1 Write / Read Length #4 (Len = 256, long form)
+mbedtls_asn1_write_len:256:"820100":3
+
+ASN.1 Write / Read Length #5 (Len = 65535, max supported length)
+mbedtls_asn1_write_len:65535:"82FFFF":3
+
+ASN.1 Write / Read Length #6 (Len = 65536, not supported)
+mbedtls_asn1_write_len:65536:"":MBEDTLS_ERR_ASN1_INVALID_LENGTH
diff --git a/tests/suites/test_suite_asn1write.function b/tests/suites/test_suite_asn1write.function
index a15c821..160190f 100644
--- a/tests/suites/test_suite_asn1write.function
+++ b/tests/suites/test_suite_asn1write.function
@@ -82,3 +82,39 @@
     }
 }
 /* END_CASE */
+
+/* BEGIN_CASE */
+void mbedtls_asn1_write_len( int len, char *check_str, int result )
+{
+    int ret;
+    unsigned char buf[150];
+    unsigned char asn1[150];
+    unsigned char *p;
+    size_t asn1_len, i;
+
+    memset( buf, GUARD_VAL, sizeof( buf ) );
+    memset( asn1, 0, sizeof( asn1 ) );
+    asn1_len = unhexify( asn1, check_str );
+
+    p = buf + GUARD_LEN + asn1_len;
+
+    ret = mbedtls_asn1_write_len( &p, buf + GUARD_LEN, (size_t) len );
+
+    TEST_ASSERT( ret == result );
+
+    /* Check for buffer overwrite on both sides */
+    for( i = 0; i < GUARD_LEN; i++ )
+    {
+        TEST_ASSERT( buf[i] == GUARD_VAL );
+        TEST_ASSERT( buf[GUARD_LEN + asn1_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( memcmp( p, asn1, asn1_len ) == 0 );
+    }
+}
+/* END_CASE */