diff --git a/tests/suites/test_suite_x509write.data b/tests/suites/test_suite_x509write.data
index 888c9ab..8d9a11a 100644
--- a/tests/suites/test_suite_x509write.data
+++ b/tests/suites/test_suite_x509write.data
@@ -58,6 +58,22 @@
 depends_on:MBEDTLS_SHA1_C:MBEDTLS_RSA_C:MBEDTLS_PKCS1_V15:MBEDTLS_DES_C:MBEDTLS_CIPHER_MODE_CBC:MBEDTLS_MD5_C
 x509_crt_check:"data_files/server1.key":"":"C=NL,O=PolarSSL,CN=PolarSSL Server 1":"data_files/test-ca.key":"PolarSSLTest":"C=NL,O=PolarSSL,CN=PolarSSL Test CA":"1":"20190210144406":"20290210144406":MBEDTLS_MD_SHA1:0:0:0:0:1:-1:"data_files/server1.crt":0:0:"data_files/test-ca.crt"
 
+Certificate write check Server1 SHA1, not before 1970
+depends_on:MBEDTLS_SHA1_C:MBEDTLS_RSA_C:MBEDTLS_PKCS1_V15:MBEDTLS_DES_C:MBEDTLS_CIPHER_MODE_CBC:MBEDTLS_MD5_C
+x509_crt_check:"data_files/server1.key":"":"C=NL,O=PolarSSL,CN=PolarSSL Server 1":"data_files/test-ca.key":"PolarSSLTest":"C=NL,O=PolarSSL,CN=PolarSSL Test CA":"1":"19700210144406":"20290210144406":MBEDTLS_MD_SHA1:0:0:0:0:1:-1:"":0:0:"data_files/test-ca.crt"
+
+Certificate write check Server1 SHA1, not after 2050
+depends_on:MBEDTLS_SHA1_C:MBEDTLS_RSA_C:MBEDTLS_PKCS1_V15:MBEDTLS_DES_C:MBEDTLS_CIPHER_MODE_CBC:MBEDTLS_MD5_C
+x509_crt_check:"data_files/server1.key":"":"C=NL,O=PolarSSL,CN=PolarSSL Server 1":"data_files/test-ca.key":"PolarSSLTest":"C=NL,O=PolarSSL,CN=PolarSSL Test CA":"1":"20190210144406":"20500210144406":MBEDTLS_MD_SHA1:0:0:0:0:1:-1:"":0:0:"data_files/test-ca.crt"
+
+Certificate write check Server1 SHA1, not before 1970, not after 2050
+depends_on:MBEDTLS_SHA1_C:MBEDTLS_RSA_C:MBEDTLS_PKCS1_V15:MBEDTLS_DES_C:MBEDTLS_CIPHER_MODE_CBC:MBEDTLS_MD5_C
+x509_crt_check:"data_files/server1.key":"":"C=NL,O=PolarSSL,CN=PolarSSL Server 1":"data_files/test-ca.key":"PolarSSLTest":"C=NL,O=PolarSSL,CN=PolarSSL Test CA":"1":"19700210144406":"20500210144406":MBEDTLS_MD_SHA1:0:0:0:0:1:-1:"":0:0:"data_files/test-ca.crt"
+
+Certificate write check Server1 SHA1, not before 2050, not after 2059
+depends_on:MBEDTLS_SHA1_C:MBEDTLS_RSA_C:MBEDTLS_PKCS1_V15:MBEDTLS_DES_C:MBEDTLS_CIPHER_MODE_CBC:MBEDTLS_MD5_C
+x509_crt_check:"data_files/server1.key":"":"C=NL,O=PolarSSL,CN=PolarSSL Server 1":"data_files/test-ca.key":"PolarSSLTest":"C=NL,O=PolarSSL,CN=PolarSSL Test CA":"1":"20500210144406":"20590210144406":MBEDTLS_MD_SHA1:0:0:0:0:1:-1:"":0:0:"data_files/test-ca.crt"
+
 Certificate write check Server1 SHA1, key_usage
 depends_on:MBEDTLS_SHA1_C:MBEDTLS_RSA_C:MBEDTLS_PKCS1_V15:MBEDTLS_DES_C:MBEDTLS_CIPHER_MODE_CBC:MBEDTLS_MD5_C
 x509_crt_check:"data_files/server1.key":"":"C=NL,O=PolarSSL,CN=PolarSSL Server 1":"data_files/test-ca.key":"PolarSSLTest":"C=NL,O=PolarSSL,CN=PolarSSL Test CA":"1":"20190210144406":"20290210144406":MBEDTLS_MD_SHA1:MBEDTLS_X509_KU_DIGITAL_SIGNATURE | MBEDTLS_X509_KU_NON_REPUDIATION | MBEDTLS_X509_KU_KEY_ENCIPHERMENT:1:0:0:1:-1:"data_files/server1.key_usage.crt":0:0:"data_files/test-ca.crt"
diff --git a/tests/suites/test_suite_x509write.function b/tests/suites/test_suite_x509write.function
index f5001bd..8f5c947 100644
--- a/tests/suites/test_suite_x509write.function
+++ b/tests/suites/test_suite_x509write.function
@@ -242,8 +242,10 @@
     mbedtls_x509write_cert crt;
     unsigned char buf[4096];
     unsigned char check_buf[5000];
+    unsigned char *p, *end;
+    unsigned char tag, sz;
     mbedtls_mpi serial;
-    int ret;
+    int ret, before_tag, after_tag;
     size_t olen = 0, pem_len = 0, buf_index = 0;
     int der_len = -1;
     FILE *f;
@@ -374,7 +376,7 @@
         TEST_EQUAL( flags, 0 );
         TEST_EQUAL( ret, 0 );
     }
-    else
+    else if( *cert_check_file != '\0' )
     {
         f = fopen( cert_check_file, "r" );
         TEST_ASSERT( f != NULL );
@@ -395,6 +397,54 @@
     if( der_len == 0 )
         goto exit;
 
+    // Not testing against file, check date format
+    if( *cert_check_file == '\0' )
+    {
+        // UTC tag if before 2050, 2 digits less for year
+        if( not_before[0] == '2' && ( not_before[1] > '0' || not_before[2] > '4' ) )
+        {
+            before_tag = MBEDTLS_ASN1_GENERALIZED_TIME;
+        }
+        else
+        {
+            before_tag = MBEDTLS_ASN1_UTC_TIME;
+            not_before += 2;
+        }
+        if( not_after[0] == '2' && ( not_after[1] > '0' || not_after[2] > '4' ) )
+        {
+            after_tag = MBEDTLS_ASN1_GENERALIZED_TIME;
+        }
+        else
+        {
+            after_tag = MBEDTLS_ASN1_UTC_TIME;
+            not_after += 2;
+        }
+        end = buf + sizeof( buf );
+        for( p = end - der_len ; p < end ; )
+        {
+            tag = *p++;
+            sz = *p++;
+            if( tag == MBEDTLS_ASN1_UTC_TIME || tag == MBEDTLS_ASN1_GENERALIZED_TIME )
+            {
+                // Check correct tag and time written
+                TEST_ASSERT( before_tag == tag );
+                TEST_ASSERT( memcmp( p, not_before, sz - 1 ) == 0 );
+                p += sz;
+                tag = *p++;
+                sz = *p++;
+                TEST_ASSERT( after_tag == tag );
+                TEST_ASSERT( memcmp( p, not_after, sz - 1 ) == 0 );
+                break;
+            }
+            // Increment if long form ASN1 length
+            if( sz & 0x80 )
+                p += sz & 0x0F;
+            if( tag != ( MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) )
+                p += sz;
+        }
+        TEST_ASSERT( p < end );
+    }
+
 #if defined(MBEDTLS_USE_PSA_CRYPTO)
     // When using PSA crypto, RNG isn't controllable, result length isn't
     // deterministic over multiple runs, removing a single byte isn't enough to