diff --git a/library/x509write_crt.c b/library/x509write_crt.c
index 32c6550..498b8b0 100644
--- a/library/x509write_crt.c
+++ b/library/x509write_crt.c
@@ -163,7 +163,7 @@
     return(
         mbedtls_x509write_crt_set_extension( ctx, MBEDTLS_OID_BASIC_CONSTRAINTS,
                              MBEDTLS_OID_SIZE( MBEDTLS_OID_BASIC_CONSTRAINTS ),
-                             0, buf + sizeof(buf) - len, len ) );
+                             is_ca, buf + sizeof(buf) - len, len ) );
 }
 
 #if defined(MBEDTLS_SHA1_C)
diff --git a/tests/data_files/Makefile b/tests/data_files/Makefile
index b90ce74..0962898 100644
--- a/tests/data_files/Makefile
+++ b/tests/data_files/Makefile
@@ -1018,6 +1018,14 @@
 	$(OPENSSL) x509 -inform PEM -in $< -outform DER -out $@
 all_final += server1.v1.crt server1.v1.der
 
+server1.ca.crt: server1.key server1.req.sha256 $(test_ca_crt) $(test_ca_key_file_rsa)
+	$(MBEDTLS_CERT_WRITE) request_file=server1.req.sha256 issuer_crt=$(test_ca_crt) issuer_key=$(test_ca_key_file_rsa) issuer_pwd=$(test_ca_pwd_rsa) version=1 not_before=20190210144406 not_after=20290210144406 md=SHA1 is_ca=1 version=3 output_file=$@
+server1.ca_noauthid.crt: server1.key server1.req.sha256 $(test_ca_crt) $(test_ca_key_file_rsa)
+	$(MBEDTLS_CERT_WRITE) request_file=server1.req.sha256 issuer_crt=$(test_ca_crt) issuer_key=$(test_ca_key_file_rsa) issuer_pwd=$(test_ca_pwd_rsa) not_before=20190210144406 not_after=20290210144406 md=SHA1 authority_identifier=0 is_ca=1 version=3 output_file=$@
+server1.ca.der: server1.ca.crt
+	$(OPENSSL) x509 -inform PEM -in $< -outform DER -out $@
+all_final += server1.ca.crt server1.ca_noauthid.crt server1.ca.der
+
 server1_ca.crt: server1.crt $(test_ca_crt)
 	cat server1.crt $(test_ca_crt) > $@
 all_final += server1_ca.crt
diff --git a/tests/data_files/server1.ca.crt b/tests/data_files/server1.ca.crt
new file mode 100644
index 0000000..84691d6
--- /dev/null
+++ b/tests/data_files/server1.ca.crt
@@ -0,0 +1,20 @@
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----
diff --git a/tests/data_files/server1.ca.der b/tests/data_files/server1.ca.der
new file mode 100644
index 0000000..a5ff059
--- /dev/null
+++ b/tests/data_files/server1.ca.der
Binary files differ
diff --git a/tests/data_files/server1.ca_noauthid.crt b/tests/data_files/server1.ca_noauthid.crt
new file mode 100644
index 0000000..e66956d
--- /dev/null
+++ b/tests/data_files/server1.ca_noauthid.crt
@@ -0,0 +1,19 @@
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----
diff --git a/tests/suites/test_suite_x509write.data b/tests/suites/test_suite_x509write.data
index b3f209e..e0f80be 100644
--- a/tests/suites/test_suite_x509write.data
+++ b/tests/suites/test_suite_x509write.data
@@ -56,35 +56,43 @@
 
 Certificate write check Server1 SHA1
 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
+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
 
 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
+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
 
 Certificate write check Server1 SHA1, ns_cert_type
 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:MBEDTLS_X509_NS_CERT_TYPE_SSL_SERVER:1:1:-1:"data_files/server1.cert_type.crt":0
+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:MBEDTLS_X509_NS_CERT_TYPE_SSL_SERVER:1:1:-1:"data_files/server1.cert_type.crt":0:0
 
 Certificate write check Server1 SHA1, version 1
 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:MBEDTLS_X509_CRT_VERSION_1:"data_files/server1.v1.crt":0
+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:MBEDTLS_X509_CRT_VERSION_1:"data_files/server1.v1.crt":0:0
+
+Certificate write check Server1 SHA1, CA
+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.ca.crt":0:1
 
 Certificate write check Server1 SHA1, RSA_ALT
 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_SHA1:0:0:0:0:0:-1:"data_files/server1.noauthid.crt":1
+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_SHA1:0:0:0:0:0:-1:"data_files/server1.noauthid.crt":1:0
 
 Certificate write check Server1 SHA1, RSA_ALT, 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:1:0:0:0:-1:"data_files/server1.key_usage_noauthid.crt":1
+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:1:0:0:0:-1:"data_files/server1.key_usage_noauthid.crt":1:0
 
 Certificate write check Server1 SHA1, RSA_ALT, ns_cert_type
 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:MBEDTLS_X509_NS_CERT_TYPE_SSL_SERVER:1:0:-1:"data_files/server1.cert_type_noauthid.crt":1
+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:MBEDTLS_X509_NS_CERT_TYPE_SSL_SERVER:1:0:-1:"data_files/server1.cert_type_noauthid.crt":1:0
 
 Certificate write check Server1 SHA1, RSA_ALT, version 1
 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_SHA1:0:0:0:0:0:MBEDTLS_X509_CRT_VERSION_1:"data_files/server1.v1.crt":1
+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_SHA1:0:0:0:0:0:MBEDTLS_X509_CRT_VERSION_1:"data_files/server1.v1.crt":1:0
+
+Certificate write check Server1 SHA1, RSA_ALT, CA
+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_SHA1:0:0:0:0:0:-1:"data_files/server1.ca_noauthid.crt":1:1
 
 
 X509 String to Names #1
diff --git a/tests/suites/test_suite_x509write.function b/tests/suites/test_suite_x509write.function
index 9b32cba..9960989 100644
--- a/tests/suites/test_suite_x509write.function
+++ b/tests/suites/test_suite_x509write.function
@@ -206,7 +206,7 @@
                      char *serial_str, char *not_before, char *not_after,
                      int md_type, int key_usage, int set_key_usage,
                      int cert_type, int set_cert_type, int auth_ident,
-                     int ver, char *cert_check_file, int rsa_alt )
+                     int ver, char *cert_check_file, int rsa_alt, int is_ca )
 {
     mbedtls_pk_context subject_key, issuer_key, issuer_key_alt;
     mbedtls_pk_context *key = &issuer_key;
@@ -269,7 +269,9 @@
 
     if( crt.version >= MBEDTLS_X509_CRT_VERSION_3 )
     {
-        TEST_ASSERT( mbedtls_x509write_crt_set_basic_constraints( &crt, 0, 0 ) == 0 );
+        /* For the CA case, a path length of -1 means unlimited. */
+        TEST_ASSERT( mbedtls_x509write_crt_set_basic_constraints( &crt, is_ca,
+                                                                  (is_ca ? -1 : 0) ) == 0 );
         TEST_ASSERT( mbedtls_x509write_crt_set_subject_key_identifier( &crt ) == 0 );
         if( auth_ident )
             TEST_ASSERT( mbedtls_x509write_crt_set_authority_key_identifier( &crt ) == 0 );