diff --git a/tests/data_files/Makefile b/tests/data_files/Makefile
index 49db4ca..34af96f 100644
--- a/tests/data_files/Makefile
+++ b/tests/data_files/Makefile
@@ -909,6 +909,11 @@
 	$(MBEDTLS_CERT_REQ) output_file=$@ filename=$< subject_name="C=NL,O=PolarSSL,CN=PolarSSL Server 1" md=SHA256
 all_final += server1.req.sha256
 
+server1.req.sha256.ext: server1.key
+	# Generating this with OpenSSL as a comparison point to test we're getting the same result
+	openssl req -new -out $@ -key $< -subj '/C=NL/O=PolarSSL/CN=PolarSSL Server 1' -sha256 -addext "extendedKeyUsage=serverAuth"
+all_final += server1.req.sha256.ext
+
 server1.req.sha384: server1.key
 	$(MBEDTLS_CERT_REQ) output_file=$@ filename=$< subject_name="C=NL,O=PolarSSL,CN=PolarSSL Server 1" md=SHA384
 all_final += server1.req.sha384
diff --git a/tests/data_files/server1.req.sha256.ext b/tests/data_files/server1.req.sha256.ext
new file mode 100644
index 0000000..3f26f09
--- /dev/null
+++ b/tests/data_files/server1.req.sha256.ext
@@ -0,0 +1,17 @@
+-----BEGIN CERTIFICATE REQUEST-----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+-----END CERTIFICATE REQUEST-----
diff --git a/tests/suites/test_suite_x509write.data b/tests/suites/test_suite_x509write.data
index 1c1cf30..aa8b3cd 100644
--- a/tests/suites/test_suite_x509write.data
+++ b/tests/suites/test_suite_x509write.data
@@ -1,54 +1,58 @@
 Certificate Request check Server1 SHA1
 depends_on:MBEDTLS_SHA1_C:MBEDTLS_RSA_C:MBEDTLS_PKCS1_V15
-x509_csr_check:"data_files/server1.key":"data_files/server1.req.sha1":MBEDTLS_MD_SHA1:0:0:0:0
+x509_csr_check:"data_files/server1.key":"data_files/server1.req.sha1":MBEDTLS_MD_SHA1:0:0:0:0:0
 
 Certificate Request check Server1 SHA224
 depends_on:MBEDTLS_SHA256_C:MBEDTLS_RSA_C:MBEDTLS_PKCS1_V15
-x509_csr_check:"data_files/server1.key":"data_files/server1.req.sha224":MBEDTLS_MD_SHA224:0:0:0:0
+x509_csr_check:"data_files/server1.key":"data_files/server1.req.sha224":MBEDTLS_MD_SHA224:0:0:0:0:0
 
 Certificate Request check Server1 SHA256
 depends_on:MBEDTLS_SHA256_C:MBEDTLS_RSA_C:MBEDTLS_PKCS1_V15
-x509_csr_check:"data_files/server1.key":"data_files/server1.req.sha256":MBEDTLS_MD_SHA256:0:0:0:0
+x509_csr_check:"data_files/server1.key":"data_files/server1.req.sha256":MBEDTLS_MD_SHA256:0:0:0:0:0
 
 Certificate Request check Server1 SHA384
 depends_on:MBEDTLS_SHA512_C:!MBEDTLS_SHA512_NO_SHA384:MBEDTLS_RSA_C:MBEDTLS_PKCS1_V15
-x509_csr_check:"data_files/server1.key":"data_files/server1.req.sha384":MBEDTLS_MD_SHA384:0:0:0:0
+x509_csr_check:"data_files/server1.key":"data_files/server1.req.sha384":MBEDTLS_MD_SHA384:0:0:0:0:0
 
 Certificate Request check Server1 SHA512
 depends_on:MBEDTLS_SHA512_C:MBEDTLS_RSA_C:MBEDTLS_PKCS1_V15
-x509_csr_check:"data_files/server1.key":"data_files/server1.req.sha512":MBEDTLS_MD_SHA512:0:0:0:0
+x509_csr_check:"data_files/server1.key":"data_files/server1.req.sha512":MBEDTLS_MD_SHA512:0:0:0:0:0
 
 Certificate Request check Server1 MD4
 depends_on:MBEDTLS_MD4_C:MBEDTLS_RSA_C:MBEDTLS_PKCS1_V15
-x509_csr_check:"data_files/server1.key":"data_files/server1.req.md4":MBEDTLS_MD_MD4:0:0:0:0
+x509_csr_check:"data_files/server1.key":"data_files/server1.req.md4":MBEDTLS_MD_MD4:0:0:0:0:0
 
 Certificate Request check Server1 MD5
 depends_on:MBEDTLS_MD5_C:MBEDTLS_RSA_C:MBEDTLS_PKCS1_V15
-x509_csr_check:"data_files/server1.key":"data_files/server1.req.md5":MBEDTLS_MD_MD5:0:0:0:0
+x509_csr_check:"data_files/server1.key":"data_files/server1.req.md5":MBEDTLS_MD_MD5:0:0:0:0:0
 
 Certificate Request check Server1 key_usage
 depends_on:MBEDTLS_SHA1_C:MBEDTLS_RSA_C:MBEDTLS_PKCS1_V15
-x509_csr_check:"data_files/server1.key":"data_files/server1.req.key_usage":MBEDTLS_MD_SHA1:MBEDTLS_X509_KU_DIGITAL_SIGNATURE | MBEDTLS_X509_KU_NON_REPUDIATION | MBEDTLS_X509_KU_KEY_ENCIPHERMENT:1:0:0
+x509_csr_check:"data_files/server1.key":"data_files/server1.req.key_usage":MBEDTLS_MD_SHA1:MBEDTLS_X509_KU_DIGITAL_SIGNATURE | MBEDTLS_X509_KU_NON_REPUDIATION | MBEDTLS_X509_KU_KEY_ENCIPHERMENT:1:0:0:0
 
 Certificate Request check Server1 key_usage empty
 depends_on:MBEDTLS_SHA1_C:MBEDTLS_RSA_C:MBEDTLS_PKCS1_V15
-x509_csr_check:"data_files/server1.key":"data_files/server1.req.key_usage_empty":MBEDTLS_MD_SHA1:0:1:0:0
+x509_csr_check:"data_files/server1.key":"data_files/server1.req.key_usage_empty":MBEDTLS_MD_SHA1:0:1:0:0:0
 
 Certificate Request check Server1 ns_cert_type
 depends_on:MBEDTLS_SHA1_C:MBEDTLS_RSA_C:MBEDTLS_PKCS1_V15
-x509_csr_check:"data_files/server1.key":"data_files/server1.req.cert_type":MBEDTLS_MD_SHA1:0:0:MBEDTLS_X509_NS_CERT_TYPE_SSL_SERVER:1
+x509_csr_check:"data_files/server1.key":"data_files/server1.req.cert_type":MBEDTLS_MD_SHA1:0:0:MBEDTLS_X509_NS_CERT_TYPE_SSL_SERVER:1:0
 
 Certificate Request check Server1 ns_cert_type empty
 depends_on:MBEDTLS_SHA1_C:MBEDTLS_RSA_C:MBEDTLS_PKCS1_V15
-x509_csr_check:"data_files/server1.key":"data_files/server1.req.cert_type_empty":MBEDTLS_MD_SHA1:0:0:0:1
+x509_csr_check:"data_files/server1.key":"data_files/server1.req.cert_type_empty":MBEDTLS_MD_SHA1:0:0:0:1:0
 
 Certificate Request check Server1 key_usage + ns_cert_type
 depends_on:MBEDTLS_SHA1_C:MBEDTLS_RSA_C:MBEDTLS_PKCS1_V15
-x509_csr_check:"data_files/server1.key":"data_files/server1.req.ku-ct":MBEDTLS_MD_SHA1:MBEDTLS_X509_KU_DIGITAL_SIGNATURE | MBEDTLS_X509_KU_NON_REPUDIATION | MBEDTLS_X509_KU_KEY_ENCIPHERMENT:1:MBEDTLS_X509_NS_CERT_TYPE_SSL_SERVER:1
+x509_csr_check:"data_files/server1.key":"data_files/server1.req.ku-ct":MBEDTLS_MD_SHA1:MBEDTLS_X509_KU_DIGITAL_SIGNATURE | MBEDTLS_X509_KU_NON_REPUDIATION | MBEDTLS_X509_KU_KEY_ENCIPHERMENT:1:MBEDTLS_X509_NS_CERT_TYPE_SSL_SERVER:1:0
 
 Certificate Request check Server5 ECDSA, key_usage
 depends_on:MBEDTLS_SHA1_C:MBEDTLS_ECDSA_C:MBEDTLS_ECDSA_DETERMINISTIC:MBEDTLS_ECP_DP_SECP256R1_ENABLED
-x509_csr_check:"data_files/server5.key":"data_files/server5.req.ku.sha1":MBEDTLS_MD_SHA1:MBEDTLS_X509_KU_DIGITAL_SIGNATURE | MBEDTLS_X509_KU_NON_REPUDIATION:1:0:0
+x509_csr_check:"data_files/server5.key":"data_files/server5.req.ku.sha1":MBEDTLS_MD_SHA1:MBEDTLS_X509_KU_DIGITAL_SIGNATURE | MBEDTLS_X509_KU_NON_REPUDIATION:1:0:0:0
+
+Certificate Request check Server1, set_extension
+depends_on:MBEDTLS_SHA256_C:MBEDTLS_RSA_C:MBEDTLS_PKCS1_V15
+x509_csr_check:"data_files/server1.key":"data_files/server1.req.sha256.ext":MBEDTLS_MD_SHA256:0:0:0:0:1
 
 Certificate Request check opaque Server5 ECDSA, key_usage
 depends_on:MBEDTLS_SHA256_C:MBEDTLS_ECDSA_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED
diff --git a/tests/suites/test_suite_x509write.function b/tests/suites/test_suite_x509write.function
index 12c8f39..b27a252 100644
--- a/tests/suites/test_suite_x509write.function
+++ b/tests/suites/test_suite_x509write.function
@@ -5,6 +5,7 @@
 #include "mbedtls/pem.h"
 #include "mbedtls/oid.h"
 #include "mbedtls/rsa.h"
+#include "mbedtls/asn1write.h"
 
 #if defined(MBEDTLS_RSA_C)
 int mbedtls_rsa_decrypt_func( void *ctx, int mode, size_t *olen,
@@ -68,6 +69,56 @@
 }
 #endif /* MBEDTLS_USE_PSA_CRYPTO && MBEDTLS_PEM_WRITE_C && MBEDTLS_X509_CSR_WRITE_C */
 
+#if defined(MBEDTLS_X509_CSR_WRITE_C)
+
+/*
+ * The size of this temporary buffer is given by the sequence of functions
+ * called hereinafter:
+ * - mbedtls_asn1_write_oid()
+ *     - 8 bytes for MBEDTLS_OID_EXTENDED_KEY_USAGE raw value
+ *     - 1 byte for MBEDTLS_OID_EXTENDED_KEY_USAGE length
+ *     - 1 byte for MBEDTLS_ASN1_OID tag
+ * - mbedtls_asn1_write_len()
+ *     - 1 byte since we're dealing with sizes which are less than 0x80
+ * - mbedtls_asn1_write_tag()
+ *     - 1 byte
+ *
+ * This length is fine as long as this function is called using the
+ * MBEDTLS_OID_SERVER_AUTH OID. If this is changed in the future, then this
+ * buffer's length should be adjusted accordingly.
+ * Unfortunately there's no predefined max size for OIDs which can be used
+ * to set an overall upper boundary which is always guaranteed.
+ */
+#define EXT_KEY_USAGE_TMP_BUF_MAX_LENGTH    12
+
+static int csr_set_extended_key_usage( mbedtls_x509write_csr *ctx,
+                        const char *oid, size_t oid_len )
+{
+    unsigned char buf[EXT_KEY_USAGE_TMP_BUF_MAX_LENGTH] = { 0 };
+    unsigned char *p = buf + sizeof( buf );
+    int ret;
+    size_t len = 0;
+
+    /*
+     * Following functions fail anyway if the temporary buffer is not large,
+     * but we set an extra check here to emphasize a possible source of errors
+     */
+    if ( oid_len > EXT_KEY_USAGE_TMP_BUF_MAX_LENGTH )
+    {
+        return MBEDTLS_ERR_X509_BAD_INPUT_DATA;
+    }
+
+    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_oid( &p, buf, oid, oid_len ) );
+    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &p, buf, ret ) );
+    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &p, buf,
+                        MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) );
+
+    ret = mbedtls_x509write_csr_set_extension( ctx, MBEDTLS_OID_EXTENDED_KEY_USAGE,
+              MBEDTLS_OID_SIZE( MBEDTLS_OID_EXTENDED_KEY_USAGE ), p, len );
+
+    return ret;
+}
+#endif  /* MBEDTLS_X509_CSR_WRITE_C */
 /* END_HEADER */
 
 /* BEGIN_DEPENDENCIES
@@ -78,7 +129,7 @@
 /* BEGIN_CASE depends_on:MBEDTLS_PEM_WRITE_C:MBEDTLS_X509_CSR_WRITE_C */
 void x509_csr_check( char * key_file, char * cert_req_check_file, int md_type,
                      int key_usage, int set_key_usage, int cert_type,
-                     int set_cert_type )
+                     int set_cert_type, int set_extension )
 {
     mbedtls_pk_context key;
     mbedtls_x509write_csr req;
@@ -105,6 +156,9 @@
         TEST_ASSERT( mbedtls_x509write_csr_set_key_usage( &req, key_usage ) == 0 );
     if( set_cert_type != 0 )
         TEST_ASSERT( mbedtls_x509write_csr_set_ns_cert_type( &req, cert_type ) == 0 );
+    if ( set_extension != 0 )
+        TEST_ASSERT( csr_set_extended_key_usage( &req, MBEDTLS_OID_SERVER_AUTH,
+                            MBEDTLS_OID_SIZE( MBEDTLS_OID_SERVER_AUTH ) ) == 0 );
 
     ret = mbedtls_x509write_csr_pem( &req, buf, sizeof( buf ),
                                      mbedtls_test_rnd_pseudo_rand, &rnd_info );