diff --git a/compat/Makefile.am b/compat/Makefile.am
index 83595cd..03f7109 100644
--- a/compat/Makefile.am
+++ b/compat/Makefile.am
@@ -98,3 +98,7 @@ if   !HAVE_ASN1_TIME_TM_CMP
 libcompat_la_SOURCES += a_time_tm.c
 endif
 endif
+
+if !HAVE_X509_GET_EXTENSION_FLAGS
+libcompat_la_SOURCES += x509_purp.c
+endif
diff --git a/compat/x509_purp.c b/compat/x509_purp.c
new file mode 100644
index 0000000..aaef3df
--- /dev/null
+++ b/compat/x509_purp.c
@@ -0,0 +1,69 @@
+/* $OpenBSD: x509_purp.c,v 1.13 2021/11/04 23:52:34 beck Exp $ */
+/* Written by Dr Stephen N Henson (steve@openssl.org) for the OpenSSL
+ * project 2001.
+ */
+/* ====================================================================
+ * Copyright (c) 1999-2004 The OpenSSL Project.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * 3. All advertising materials mentioning features or use of this
+ *    software must display the following acknowledgment:
+ *    "This product includes software developed by the OpenSSL Project
+ *    for use in the OpenSSL Toolkit. (http://www.OpenSSL.org/)"
+ *
+ * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
+ *    endorse or promote products derived from this software without
+ *    prior written permission. For written permission, please contact
+ *    licensing@OpenSSL.org.
+ *
+ * 5. Products derived from this software may not be called "OpenSSL"
+ *    nor may "OpenSSL" appear in their names without prior written
+ *    permission of the OpenSSL Project.
+ *
+ * 6. Redistributions of any form whatsoever must retain the following
+ *    acknowledgment:
+ *    "This product includes software developed by the OpenSSL Project
+ *    for use in the OpenSSL Toolkit (http://www.OpenSSL.org/)"
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
+ * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
+ * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ * ====================================================================
+ *
+ * This product includes cryptographic software written by Eric Young
+ * (eay@cryptsoft.com).  This product includes software written by Tim
+ * Hudson (tjh@cryptsoft.com).
+ *
+ */
+
+#include <openssl/x509v3.h>
+
+uint32_t
+X509_get_extension_flags(X509 *x)
+{
+	/* Call for side-effect of computing hash and caching extensions */
+	if (X509_check_purpose(x, -1, -1) != 1)
+		return 0;
+
+	return x->ex_flags;
+}
diff --git a/configure.ac b/configure.ac
index e5b5a8f..5956063 100644
--- a/configure.ac
+++ b/configure.ac
@@ -265,9 +265,10 @@ AC_CHECK_HEADERS([openssl/cms.h openssl/err.h openssl/evp.h openssl/ssl.h openss
 AC_CHECK_LIB([crypto], [ASN1_STRING_get0_data], [], [AC_MSG_ERROR([OpenSSL libraries required])])
 AC_CHECK_FUNCS([X509_up_ref], [], [AC_MSG_ERROR([OpenSSL libraries required])])
 
-AC_CHECK_FUNCS([ASN1_time_parse ASN1_time_tm_cmp])
+AC_CHECK_FUNCS([ASN1_time_parse ASN1_time_tm_cmp X509_get_extension_flags])
 AM_CONDITIONAL([HAVE_ASN1_TIME_PARSE], [test "x$ac_cv_func_ASN1_time_parse" = xyes])
 AM_CONDITIONAL([HAVE_ASN1_TIME_TM_CMP], [test "x$ac_cv_func_ASN1_time_tm_cmp" = xyes])
+AM_CONDITIONAL([HAVE_X509_GET_EXTENSION_FLAGS], [test "x$ac_cv_func_X509_get_extension_flags" = xyes])
 
 AC_CHECK_HEADERS([tls.h], [], [AC_MSG_ERROR([LibreSSL libtls headers required])])
 AC_SEARCH_LIBS([tls_read],[tls-standalone tls retls], [], [AC_MSG_ERROR([LibreSSL libtls library required])], [-lssl -lcrypto])
diff --git a/include/Makefile.am b/include/Makefile.am
index 810f109..d821cd8 100644
--- a/include/Makefile.am
+++ b/include/Makefile.am
@@ -6,6 +6,7 @@ noinst_HEADERS += sys/tree.h
 noinst_HEADERS += sys/types.h
 noinst_HEADERS += sys/wait.h
 noinst_HEADERS += openssl/asn1.h
+noinst_HEADERS += openssl/x509v3.h
 noinst_HEADERS += imsg.h
 noinst_HEADERS += poll.h
 noinst_HEADERS += sha2.h
diff --git a/include/openssl/x509v3.h b/include/openssl/x509v3.h
new file mode 100644
index 0000000..5623397
--- /dev/null
+++ b/include/openssl/x509v3.h
@@ -0,0 +1,15 @@
+/*
+ * Public domain
+ * openssl/x509v3.h compatibility shim
+ */
+
+#include_next <openssl/x509v3.h>
+
+#ifndef LIBCOMPAT_OPENSSL_X509V3_H
+#define LIBCOMPAT_OPENSSL_X509V3_H
+
+#ifndef HAVE_X509_GET_EXTENSION_FLAGS
+uint32_t X509_get_extension_flags(X509 *x);
+#endif
+
+#endif