diff --git a/lib/krb5/Makefile.am b/lib/krb5/Makefile.am
index e93184218..506155ee3 100644
--- a/lib/krb5/Makefile.am
+++ b/lib/krb5/Makefile.am
@@ -50,7 +50,8 @@ TESTS =						\
 
 check_DATA = test_config_strings.out
 
-check_PROGRAMS = $(TESTS) test_hostname test_ap-req test_canon test_set_kvno0
+check_PROGRAMS = $(TESTS) test_hostname test_ap-req test_canon test_set_kvno0 \
+		test_mkforwardable
 
 LDADD = libkrb5.la \
 	$(LIB_hcrypto) \
diff --git a/lib/krb5/test_mkforwardable.c b/lib/krb5/test_mkforwardable.c
new file mode 100644
index 000000000..3f25f1354
--- /dev/null
+++ b/lib/krb5/test_mkforwardable.c
@@ -0,0 +1,191 @@
+/*
+ * Copyright (c) 1997-2021 Kungliga Tekniska Högskolan
+ * (Royal Institute of Technology, Stockholm, Sweden).
+ * Copyright (c) 2021 Isaac Boukris
+ * 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. Neither the name of the Institute nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS 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 INSTITUTE OR 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.
+ */
+
+#include "krb5_locl.h"
+
+/*
+ * Usage: mkforwardable server out_ccache
+ *
+ * The default cache contains a ticket to server and the default keytab
+ * contains a key to decrypt it, the ticket is decrypted and the forwardable
+ * flag is added, the ticket is then re-encrypted and stored in out_cache.
+ *
+ */
+
+static krb5_context context;
+
+static void
+check(krb5_error_code code)
+{
+    const char *errmsg;
+
+    if (code == 0)
+	return;
+
+    errmsg = krb5_get_error_message(context, code);
+    fprintf(stderr, "%s\n", errmsg);
+    krb5_free_error_message(context, errmsg);
+
+    abort();
+}
+
+static void
+decrypt_ticket_enc_part(EncryptionKey *key,
+			krb5_enctype etype,
+			Ticket *ticket,
+			EncTicketPart *et)
+{
+    krb5_error_code ret;
+    krb5_data plain;
+    size_t len;
+    krb5_crypto crypto;
+
+    check(krb5_crypto_init(context, key, etype, &crypto));
+
+    ret = krb5_decrypt_EncryptedData (context,
+				      crypto,
+				      KRB5_KU_TICKET,
+				      &ticket->enc_part,
+				      &plain);
+    check(ret);
+
+    check(decode_EncTicketPart(plain.data, plain.length, et, &len));
+
+    krb5_data_free (&plain);
+    krb5_crypto_destroy(context, crypto);
+}
+
+static void
+encrypt_ticket_enc_part(EncryptionKey *key,
+			krb5_enctype etype,
+			krb5_kvno skvno,
+			EncTicketPart *et,
+			Ticket *ticket)
+{
+    size_t len, size;
+    char *buf;
+    krb5_error_code ret;
+    krb5_crypto crypto;
+
+    ASN1_MALLOC_ENCODE(EncTicketPart, buf, len, et, &size, ret);
+    check(ret);
+
+    check(krb5_crypto_init(context, key, etype, &crypto));
+    ret = krb5_encrypt_EncryptedData(context,
+				      crypto,
+				      KRB5_KU_TICKET,
+				      buf,
+				      len,
+				      skvno,
+				      &ticket->enc_part);
+    check(ret);
+
+    free(buf);
+    krb5_crypto_destroy(context, crypto);
+}
+
+
+int
+main(int argc, char **argv)
+{
+    krb5_error_code ret;
+    krb5_keytab kt;
+    krb5_keytab_entry entry;
+    krb5_enctype etype;
+    krb5_creds mc, cred;
+    krb5_ccache ccache;
+    EncTicketPart et;
+    Ticket ticket;
+    size_t size;
+    krb5_kvno kvno = 0;
+
+    memset(&cred, 0, sizeof(cred));
+
+    if (argc != 3)
+	errx(1, "Usage: mkforwardable server out_ccache");
+
+    ret = krb5_init_context(&context);
+    if (ret)
+	errx(1, "krb5_init_context failed: %u", ret);
+
+    check(krb5_cc_default(context, &ccache));
+
+    krb5_cc_clear_mcred(&mc);
+
+    check(krb5_parse_name(context, argv[1], &mc.server));
+
+    check(krb5_cc_retrieve_cred(context, ccache, 0, &mc, &cred));
+
+    check(decode_Ticket(cred.ticket.data, cred.ticket.length, &ticket, NULL));
+
+    etype = ticket.enc_part.etype;
+
+    if (ticket.enc_part.kvno != NULL)
+	kvno = *ticket.enc_part.kvno;
+
+    check(krb5_kt_default(context, &kt));
+
+    check(krb5_kt_get_entry(context, kt, mc.server, kvno, etype, &entry));
+
+    decrypt_ticket_enc_part(&entry.keyblock, etype, &ticket, &et);
+
+    et.flags.forwardable = 1;
+    cred.flags.b = et.flags;
+
+    free_EncryptedData(&ticket.enc_part);
+
+    encrypt_ticket_enc_part(&entry.keyblock, etype, kvno, &et, &ticket);
+
+    krb5_data_free(&cred.ticket);
+    ASN1_MALLOC_ENCODE(Ticket, cred.ticket.data, cred.ticket.length, &ticket,
+		       &size, ret);
+    check(ret);
+
+    krb5_cc_close(context, ccache);
+
+    check(krb5_cc_resolve(context, argv[2], &ccache));
+    check(krb5_cc_initialize(context, ccache, cred.client));
+
+    check(krb5_cc_store_cred(context, ccache, &cred));
+
+    free_Ticket(&ticket);
+    free_EncTicketPart(&et);
+    krb5_cc_close(context, ccache);
+    krb5_free_principal(context, mc.server);
+    krb5_free_cred_contents(context, &cred);
+    krb5_kt_free_entry(context, &entry);
+    krb5_kt_close(context, kt);
+
+    return 0;
+}
diff --git a/tests/bin/setup-env.in b/tests/bin/setup-env.in
index 5c4b91852..954a2c1d5 100644
--- a/tests/bin/setup-env.in
+++ b/tests/bin/setup-env.in
@@ -58,6 +58,7 @@ rkvis="${TESTS_ENVIRONMENT} ${top_builddir}/lib/roken/rkvis"
 test_set_kvno0="${TESTS_ENVIRONMENT} ${top_builddir}/lib/krb5/test_set_kvno0"
 test_alname="${TESTS_ENVIRONMENT} ${top_builddir}/lib/krb5/test_alname"
 test_kuserok="${TESTS_ENVIRONMENT} ${top_builddir}/lib/krb5/test_kuserok"
+test_mkforwardable="${TESTS_ENVIRONMENT} ${top_builddir}/lib/krb5/test_mkforwardable"
 
 # misc apps
 have_db="${top_builddir}/tests/db/have-db"
diff --git a/tests/kdc/check-kdc.in b/tests/kdc/check-kdc.in
index d7471661f..83e717d54 100644
--- a/tests/kdc/check-kdc.in
+++ b/tests/kdc/check-kdc.in
@@ -89,6 +89,7 @@ icache="FILE:${objdir}/icache.krb5"
 keytabfile=${objdir}/server.keytab
 keytab="FILE:${keytabfile}"
 ps="proxy-service@${R}"
+rps="restricted-proxy-service@${R}"
 aesenctype="aes256-cts-hmac-sha1-96"
 
 kinit="${kinit} -c $cache ${afs_no_afslog}"
@@ -225,6 +226,11 @@ ${kadmin} modify --constrained-delegation=${server} ${ps} || exit 1
 ${kadmin} ext -k ${keytab} ${server}@${R} || exit 1
 ${kadmin} ext -k ${keytab} ${ps} || exit 1
 
+# Note: rps is not trusted-for-delegation
+${kadmin} add -p foo --use-defaults ${rps} || exit 1
+${kadmin} modify --constrained-delegation=${server} ${rps} || exit 1
+${kadmin} ext -k ${keytab} ${rps} || exit 1
+
 ${kadmin} add -p kaka --use-defaults ${server2}@${R2} || exit 1
 ${kadmin} ext -k ${keytab} ${server2}@${R2} || exit 1
 ${kadmin} add -p kaka --use-defaults ${serverip}@${R} || exit 1
@@ -906,6 +912,46 @@ ${kgetcred} --out-cache=${o2cache} --delegation-credential-cache=${ocache} ${ser
 
 ${kdestroy}
 
+echo "test constrained delegation NOT trusted-for-delegation (evidence from TGS)"; > messages.log
+
+${kinit} --forwardable --password-file=${objdir}/foopassword ${rps} || \
+	{ ec=1 ; eval "${testfailed}"; }
+${kinit} --cache=${icache} --forwardable --password-file=${objdir}/barpassword bar@${R} || \
+        { ec=1 ; eval "${testfailed}"; }
+${kgetcred} --cache=${icache} --out-cache=${ocache} ${rps} || \
+	{ ec=1 ; eval "${testfailed}"; }
+${kgetcred} \
+	--out-cache=${o2cache} \
+	--delegation-credential-cache=${ocache} \
+	${server}@${R} || \
+	{ ec=1 ; eval "${testfailed}"; }
+${test_ap_req} ${server}@${R} ${keytab} ${o2cache} || \
+	{ ec=1 ; eval "${testfailed}"; }
+
+echo "test constrained delegation NOT trusted-for-delegation (evidence from impersonate, negative)"; > messages.log
+rm -f ocache.krb5
+${kgetcred_imp} --impersonate=bar@${R} ${rps} || \
+	{ ec=1 ; eval "${testfailed}"; }
+${test_ap_req} ${rps} ${keytab} ${ocache} || \
+	{ ec=1 ; eval "${testfailed}"; }
+${kgetcred} \
+	--out-cache=${o2cache} \
+	--delegation-credential-cache=${ocache} \
+	${server}@${R} && \
+	{ ec=1 ; eval "${testfailed}"; }
+
+echo "test constrained delegation bronze-bit attack, aka CVE-2020-17049"; > messages.log
+
+KRB5CCNAME=${ocache} KRB5_KTNAME=${keytab} ${test_mkforwardable} ${rps} ${icache} || \
+{ ec=1 ; eval "${testfailed}"; }
+
+${kgetcred} \
+	--out-cache=${o2cache} \
+	--delegation-credential-cache=${icache} \
+	${server}@${R} && \
+	{ ec=1 ; eval "${testfailed}"; }
+${kdestroy}
+
 echo "check renewing" > messages.log
 ${kinit} --renewable --password-file=${objdir}/foopassword foo@$R || \
 	{ ec=1 ; eval "${testfailed}"; }