diff --git a/ChangeLog.d/issue4386.txt b/ChangeLog.d/issue4386.txt
new file mode 100644
index 0000000..9e61fdb
--- /dev/null
+++ b/ChangeLog.d/issue4386.txt
@@ -0,0 +1,3 @@
+Removals
+   * Remove the MBEDTLS_X509_ALLOW_EXTENSIONS_NON_V3 option and let the code
+     behave as if it was always disabled. Fixes #4386.
diff --git a/docs/3.0-migration-guide.d/remove_supp_for_extensions_in_pre-v3_X_509_certs.md b/docs/3.0-migration-guide.d/remove_supp_for_extensions_in_pre-v3_X_509_certs.md
new file mode 100644
index 0000000..8484dfb
--- /dev/null
+++ b/docs/3.0-migration-guide.d/remove_supp_for_extensions_in_pre-v3_X_509_certs.md
@@ -0,0 +1,11 @@
+Remove the `MBEDTLS_X509_ALLOW_EXTENSIONS_NON_V3` option
+--
+
+This change does not affect users who are working with current V3 X.509
+certificates.
+
+This change makes the pre-V3 X.509 certificates both with or without optional
+extensions obsolete.
+
+If you are working with the pre-V3 certificates you need to switch to the
+current ones.
diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index 1014091..f4d76e6 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -1939,16 +1939,6 @@
 #define MBEDTLS_VERSION_FEATURES
 
 /**
- * \def MBEDTLS_X509_ALLOW_EXTENSIONS_NON_V3
- *
- * If set, the X509 parser will not break-off when parsing an X509 certificate
- * and encountering an extension in a v1 or v2 certificate.
- *
- * Uncomment to prevent an error.
- */
-//#define MBEDTLS_X509_ALLOW_EXTENSIONS_NON_V3
-
-/**
  * \def MBEDTLS_X509_ALLOW_UNSUPPORTED_CRITICAL_EXTENSION
  *
  * If set, the X509 parser will not break-off when parsing an X509 certificate
diff --git a/library/x509_crt.c b/library/x509_crt.c
index b4fe886..8387de6 100644
--- a/library/x509_crt.c
+++ b/library/x509_crt.c
@@ -1268,9 +1268,7 @@
         }
     }
 
-#if !defined(MBEDTLS_X509_ALLOW_EXTENSIONS_NON_V3)
     if( crt->version == 3 )
-#endif
     {
         ret = x509_get_crt_ext( &p, end, crt, cb, p_ctx );
         if( ret != 0 )
diff --git a/tests/suites/test_suite_x509parse.data b/tests/suites/test_suite_x509parse.data
index 8b7b09a..59acc66 100644
--- a/tests/suites/test_suite_x509parse.data
+++ b/tests/suites/test_suite_x509parse.data
@@ -178,10 +178,6 @@
 depends_on:MBEDTLS_PEM_PARSE_C:MBEDTLS_RSA_C:MBEDTLS_SHA256_C
 x509_cert_info:"data_files/non-ascii-string-in-issuer.crt":"cert. version     \: 3\nserial number     \: 05\:E6\:53\:E7\:1B\:74\:F0\:B5\:D3\:84\:6D\:0C\:6D\:DC\:FA\:3F\:A4\:5A\:2B\:E0\nissuer name       \: C=JP, ST=Tokyo, O=?????????????????? Ltd, CN=?????????????????? CA\nsubject name      \: C=JP, ST=Tokyo, O=?????????????????? Ltd, CN=?????????????????? CA\nissued  on        \: 2020-05-20 16\:17\:23\nexpires on        \: 2020-06-19 16\:17\:23\nsigned using      \: RSA with SHA-256\nRSA key size      \: 2048 bits\nbasic constraints \: CA=true\n"
 
-X509 certificate v1 with extension
-depends_on:MBEDTLS_PEM_PARSE_C:MBEDTLS_RSA_C:MBEDTLS_X509_ALLOW_EXTENSIONS_NON_V3:MBEDTLS_SHA1_C
-x509_cert_info:"data_files/cert_v1_with_ext.crt":"cert. version     \: 1\nserial number     \: BD\:ED\:44\:C7\:D2\:3E\:C2\:A4\nissuer name       \: C=XX, ST=XX, L=XX, O=XX, OU=XX, emailAddress=admin@identity-check.org, CN=identity-check.org\nsubject name      \: C=XX, ST=XX, L=XX, O=XX, OU=XX, emailAddress=admin@identity-check.org, CN=identity-check.org\nissued  on        \: 2013-07-04 16\:17\:02\nexpires on        \: 2014-07-04 16\:17\:02\nsigned using      \: RSA with SHA1\nRSA key size      \: 2048 bits\nsubject alt name  \:\n    dNSName \: identity-check.org\n    dNSName \: www.identity-check.org\n    <unsupported>\n"
-
 X509 SAN parsing otherName
 depends_on:MBEDTLS_PEM_PARSE_C:MBEDTLS_ECDSA_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED:MBEDTLS_SHA256_C
 x509_parse_san:"data_files/server5-othername.crt":"type \: 0\notherName \: hardware module name \: hardware type \: 1.3.6.1.4.1.17.3, hardware serial number \: 123456\n"
@@ -1575,7 +1571,7 @@
 x509parse_crt:"308198308182a0030201028204deadbeef300d06092a864886f70d01010b0500300c310a30080600130454657374301c170c303930313031303030303030170c303931323331323335393539300c310a30080600130454657374302a300d06092A864886F70D010101050003190030160210ffffffffffffffffffffffffffffffff0202ffffa201300d06092a864886f70d01010b0500030200ff":"":MBEDTLS_ERR_X509_INVALID_FORMAT + MBEDTLS_ERR_ASN1_OUT_OF_DATA
 
 X509 CRT ASN1 (TBS, valid IssuerID, inv SubjectID, inv tag)
-depends_on:!MBEDTLS_X509_ALLOW_EXTENSIONS_NON_V3:MBEDTLS_RSA_C:MBEDTLS_SHA256_C
+depends_on:MBEDTLS_RSA_C:MBEDTLS_SHA256_C
 x509parse_crt:"30819a308184a0030201008204deadbeef300d06092a864886f70d01010b0500300c310a30080600130454657374301c170c303930313031303030303030170c303931323331323335393539300c310a30080600130454657374302a300d06092A864886F70D010101050003190030160210ffffffffffffffffffffffffffffffff0202ffffa1000500300d06092a864886f70d01010b0500030200ff":"":MBEDTLS_ERR_X509_INVALID_FORMAT + MBEDTLS_ERR_ASN1_LENGTH_MISMATCH
 
 X509 CRT ASN1 (TBSCertificate v3, ext SubjectAlternativeName malformed)
@@ -1595,21 +1591,13 @@
 x509parse_crt:"30819a308184a0030201028204deadbeef300d06092a864886f70d01010b0500300c310a30080600130454657374301c170c303930313031303030303030170c303931323331323335393539300c310a30080600130454657374302a300d06092A864886F70D010101050003190030160210ffffffffffffffffffffffffffffffff0202ffffa100a201300d06092a864886f70d01010b0500030200ff":"":MBEDTLS_ERR_X509_INVALID_FORMAT + MBEDTLS_ERR_ASN1_OUT_OF_DATA
 
 X509 CRT ASN1 (TBS, IssuerID unsupported in v1 CRT)
-depends_on:!MBEDTLS_X509_ALLOW_EXTENSIONS_NON_V3:MBEDTLS_RSA_C:MBEDTLS_SHA256_C
+depends_on:MBEDTLS_RSA_C:MBEDTLS_SHA256_C
 x509parse_crt:"30819a308184a0030201008204deadbeef300d06092a864886f70d01010b0500300c310a30080600130454657374301c170c303930313031303030303030170c303931323331323335393539300c310a30080600130454657374302a300d06092A864886F70D010101050003190030160210ffffffffffffffffffffffffffffffff0202ffffa100a201300d06092a864886f70d01010b0500030200ff":"":MBEDTLS_ERR_X509_INVALID_FORMAT + MBEDTLS_ERR_ASN1_LENGTH_MISMATCH
 
-X509 CRT ASN1 (TBS, IssuerID unsupported in v1 CRT, ALLOW_EXTENSIONS_NON_V3)
-depends_on:MBEDTLS_X509_ALLOW_EXTENSIONS_NON_V3:MBEDTLS_RSA_C:MBEDTLS_SHA256_C
-x509parse_crt:"30819a308184a0030201008204deadbeef300d06092a864886f70d01010b0500300c310a30080600130454657374301c170c303930313031303030303030170c303931323331323335393539300c310a30080600130454657374302a300d06092A864886F70D010101050003190030160210ffffffffffffffffffffffffffffffff0202ffffa100a201300d06092a864886f70d01010b0500030200ff":"":MBEDTLS_ERR_X509_INVALID_EXTENSIONS + MBEDTLS_ERR_ASN1_UNEXPECTED_TAG
-
 X509 CRT ASN1 (TBS, SubjectID unsupported in v1 CRT)
-depends_on:!MBEDTLS_X509_ALLOW_EXTENSIONS_NON_V3:MBEDTLS_RSA_C:MBEDTLS_SHA256_C
+depends_on:MBEDTLS_RSA_C:MBEDTLS_SHA256_C
 x509parse_crt:"30819a308184a0030201008204deadbeef300d06092a864886f70d01010b0500300c310a30080600130454657374301c170c303930313031303030303030170c303931323331323335393539300c310a30080600130454657374302a300d06092A864886F70D010101050003190030160210ffffffffffffffffffffffffffffffff0202ffffa200a201300d06092a864886f70d01010b0500030200ff":"":MBEDTLS_ERR_X509_INVALID_FORMAT + MBEDTLS_ERR_ASN1_LENGTH_MISMATCH
 
-X509 CRT ASN1 (TBS, SubjectID unsupported in v1 CRT, ALLOW_EXTENSIONS_NON_V3)
-depends_on:MBEDTLS_X509_ALLOW_EXTENSIONS_NON_V3:MBEDTLS_RSA_C:MBEDTLS_SHA256_C
-x509parse_crt:"30819a308184a0030201008204deadbeef300d06092a864886f70d01010b0500300c310a30080600130454657374301c170c303930313031303030303030170c303931323331323335393539300c310a30080600130454657374302a300d06092A864886F70D010101050003190030160210ffffffffffffffffffffffffffffffff0202ffffa200a201300d06092a864886f70d01010b0500030200ff":"":MBEDTLS_ERR_X509_INVALID_EXTENSIONS + MBEDTLS_ERR_ASN1_UNEXPECTED_TAG
-
 X509 CRT ASN1 (TBS, inv v3Ext, inv tag)
 depends_on:MBEDTLS_RSA_C:MBEDTLS_SHA256_C
 x509parse_crt:"30819c308186a0030201028204deadbeef300d06092a864886f70d01010b0500300c310a30080600130454657374301c170c303930313031303030303030170c303931323331323335393539300c310a30080600130454657374302a300d06092A864886F70D010101050003190030160210ffffffffffffffffffffffffffffffff0202ffffa100a2000500300d06092a864886f70d01010b0500030200ff":"":MBEDTLS_ERR_X509_INVALID_EXTENSIONS + MBEDTLS_ERR_ASN1_UNEXPECTED_TAG
@@ -1858,24 +1846,16 @@
 depends_on:MBEDTLS_RSA_C:MBEDTLS_SHA256_C
 x509parse_crt:"3081dc3081c6a0030201028204deadbeef300d06092a864886f70d01010b0500300c310a30080600130454657374301c170c303930313031303030303030170c303931323331323335393539300c310a30080600130454657374302a300d06092A864886F70D010101050003190030160210ffffffffffffffffffffffffffffffff0202ffffa100a200a321301f301d0603551d11041630148208666f6f2e7465737482086261722e74657374301d0603551d11041630148208666f6f2e7465737482086261722e74657374300d06092a864886f70d01010b0500030200ff":"":MBEDTLS_ERR_X509_INVALID_FORMAT + MBEDTLS_ERR_ASN1_LENGTH_MISMATCH
 
-X509 CRT (TBS, valid v3Ext in v1 CRT, ALLOW_EXTENSIONS_NON_V3)
-depends_on:MBEDTLS_X509_ALLOW_EXTENSIONS_NON_V3:MBEDTLS_RSA_C:MBEDTLS_SHA256_C
-x509parse_crt:"3081b93081a3a0030201008204deadbeef300d06092a864886f70d01010b0500300c310a30080600130454657374301c170c303930313031303030303030170c303931323331323335393539300c310a30080600130454657374302a300d06092A864886F70D010101050003190030160210ffffffffffffffffffffffffffffffff0202ffffa321301f301d0603551d11041630148208666f6f2e7465737482086261722e74657374300d06092a864886f70d01010b0500030200ff":"cert. version     \: 1\nserial number     \: DE\:AD\:BE\:EF\nissuer name       \: ??=Test\nsubject name      \: ??=Test\nissued  on        \: 2009-01-01 00\:00\:00\nexpires on        \: 2009-12-31 23\:59\:59\nsigned using      \: RSA with SHA-256\nRSA key size      \: 128 bits\nsubject alt name  \:\n    dNSName \: foo.test\n    dNSName \: bar.test\n":0
-
-X509 CRT (TBS, valid v3Ext in v2 CRT, ALLOW_EXTENSIONS_NON_V3)
-depends_on:MBEDTLS_X509_ALLOW_EXTENSIONS_NON_V3:MBEDTLS_RSA_C:MBEDTLS_SHA256_C
-x509parse_crt:"3081b93081a3a0030201018204deadbeef300d06092a864886f70d01010b0500300c310a30080600130454657374301c170c303930313031303030303030170c303931323331323335393539300c310a30080600130454657374302a300d06092A864886F70D010101050003190030160210ffffffffffffffffffffffffffffffff0202ffffa321301f301d0603551d11041630148208666f6f2e7465737482086261722e74657374300d06092a864886f70d01010b0500030200ff":"cert. version     \: 2\nserial number     \: DE\:AD\:BE\:EF\nissuer name       \: ??=Test\nsubject name      \: ??=Test\nissued  on        \: 2009-01-01 00\:00\:00\nexpires on        \: 2009-12-31 23\:59\:59\nsigned using      \: RSA with SHA-256\nRSA key size      \: 128 bits\nsubject alt name  \:\n    dNSName \: foo.test\n    dNSName \: bar.test\n":0
-
 X509 CRT (TBS, valid v3Ext in v3 CRT)
 depends_on:MBEDTLS_RSA_C:MBEDTLS_SHA256_C
 x509parse_crt:"3081b93081a3a0030201028204deadbeef300d06092a864886f70d01010b0500300c310a30080600130454657374301c170c303930313031303030303030170c303931323331323335393539300c310a30080600130454657374302a300d06092A864886F70D010101050003190030160210ffffffffffffffffffffffffffffffff0202ffffa321301f301d0603551d11041630148208666f6f2e7465737482086261722e74657374300d06092a864886f70d01010b0500030200ff":"cert. version     \: 3\nserial number     \: DE\:AD\:BE\:EF\nissuer name       \: ??=Test\nsubject name      \: ??=Test\nissued  on        \: 2009-01-01 00\:00\:00\nexpires on        \: 2009-12-31 23\:59\:59\nsigned using      \: RSA with SHA-256\nRSA key size      \: 128 bits\nsubject alt name  \:\n    dNSName \: foo.test\n    dNSName \: bar.test\n":0
 
 X509 CRT ASN1 (TBS, valid v3Ext in v1 CRT)
-depends_on:!MBEDTLS_X509_ALLOW_EXTENSIONS_NON_V3:MBEDTLS_RSA_C:MBEDTLS_SHA256_C
+depends_on:MBEDTLS_RSA_C:MBEDTLS_SHA256_C
 x509parse_crt:"3081b93081a3a0030201008204deadbeef300d06092a864886f70d01010b0500300c310a30080600130454657374301c170c303930313031303030303030170c303931323331323335393539300c310a30080600130454657374302a300d06092A864886F70D010101050003190030160210ffffffffffffffffffffffffffffffff0202ffffa321301f301d0603551d11041630148208666f6f2e7465737482086261722e74657374300d06092a864886f70d01010b0500030200ff":"":MBEDTLS_ERR_X509_INVALID_FORMAT + MBEDTLS_ERR_ASN1_LENGTH_MISMATCH
 
 X509 CRT ASN1 (TBS, valid v3Ext in v2 CRT)
-depends_on:!MBEDTLS_X509_ALLOW_EXTENSIONS_NON_V3:MBEDTLS_RSA_C:MBEDTLS_SHA256_C
+depends_on:MBEDTLS_RSA_C:MBEDTLS_SHA256_C
 x509parse_crt:"3081b93081a3a0030201018204deadbeef300d06092a864886f70d01010b0500300c310a30080600130454657374301c170c303930313031303030303030170c303931323331323335393539300c310a30080600130454657374302a300d06092A864886F70D010101050003190030160210ffffffffffffffffffffffffffffffff0202ffffa321301f301d0603551d11041630148208666f6f2e7465737482086261722e74657374300d06092a864886f70d01010b0500030200ff":"":MBEDTLS_ERR_X509_INVALID_FORMAT + MBEDTLS_ERR_ASN1_LENGTH_MISMATCH
 
 X509 CRT ASN1 (TBS, valid SubjectID, valid IssuerID, inv v3Ext, SubjectAltName repeated outside Extensions, inv SubjectAltNames tag)