diff --git a/dovecot-configure-c99.patch b/dovecot-configure-c99.patch
new file mode 100644
index 0000000..17a49fe
--- /dev/null
+++ b/dovecot-configure-c99.patch
@@ -0,0 +1,25 @@
+m4: crypt_xxpg6.m4: Define _DEFAULT_SOURCE for current glibc
+
+Current glibc no longer implements the CRYPT extension, so it does not
+declare crypt in <unistd.h> in strict standard modes.  The check
+defines _XOPEN_SOURCE, which enables one of these modes.  Defining
+_DEFAULT_SOURCE as well again makes available the crypt function
+prototype.
+
+This avoids a configure check result change with compilers which do
+not support implicit function declarations.
+
+Submitted upstream: <https://github.com/dovecot/core/pull/193>
+
+diff --git a/m4/crypt_xpg6.m4 b/m4/crypt_xpg6.m4
+index 0085b2ac76..3a288a3713 100644
+--- a/m4/crypt_xpg6.m4
++++ b/m4/crypt_xpg6.m4
+@@ -6,6 +6,7 @@ AC_DEFUN([DOVECOT_CRYPT_XPG6], [
+       #define _XOPEN_SOURCE 4
+       #define _XOPEN_SOURCE_EXTENDED 1
+       #define _XOPEN_VERSION 4
++      #define _DEFAULT_SOURCE
+       #define _XPG4_2
+       #define _XPG6
+       #include <unistd.h>
diff --git a/dovecot.spec b/dovecot.spec
index 3322958..477cac5 100644
--- a/dovecot.spec
+++ b/dovecot.spec
@@ -6,7 +6,7 @@ Name: dovecot
 Epoch: 1
 Version: 2.3.19.1
 %global prever %{nil}
-Release: 7%{?dist}
+Release: 8%{?dist}
 #dovecot itself is MIT, a few sources are PD, pigeonhole is LGPLv2
 License: MIT and LGPLv2
 
@@ -45,6 +45,7 @@ Patch17: dovecot-2.3.15-fixvalcond.patch
 Patch18: dovecot-2.3.15-valbasherr.patch
 Patch20: dovecot-2.3.14-opensslv3.patch
 Patch21:	dovecot-2.3.19.1-7bad6a24.patch
+Patch22: dovecot-configure-c99.patch
 
 Source15: prestartscript
 
@@ -145,6 +146,7 @@ This package provides the development files for dovecot.
 %patch18 -p1 -b .valbasherr
 %patch20 -p1 -b .opensslv3
 %patch21 -p1 -b .7bad6a24
+%patch22 -p1 -b .c99
 cp run-test-valgrind.supp dovecot-2.3-pigeonhole-%{pigeonholever}/
 # valgrind would fail with shell wrapper
 echo "testsuite" >dovecot-2.3-pigeonhole-%{pigeonholever}/run-test-valgrind.exclude
@@ -480,6 +482,9 @@ make check
 %{_libdir}/%{name}/dict/libdriver_pgsql.so
 
 %changelog
+* Mon Jan 02 2023 Florian Weimer <fweimer@redhat.com> - 1:2.3.19.1-8
+- Port configure script to C99
+
 * Sat Dec 31 2022 Pete Walter <pwalter@fedoraproject.org> - 1:2.3.19.1-7
 - Rebuild for ICU 72