diff --git a/app-crypt/coolkey/coolkey-1.1.0-r9.ebuild b/app-crypt/coolkey/coolkey-1.1.0-r9.ebuild
index cd3d7f1e434b2..d388df3391b79 100644
--- a/app-crypt/coolkey/coolkey-1.1.0-r9.ebuild
+++ b/app-crypt/coolkey/coolkey-1.1.0-r9.ebuild
@@ -1,4 +1,4 @@
-# Copyright 1999-2021 Gentoo Authors
+# Copyright 1999-2022 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2
 
 EAPI=7
@@ -26,6 +26,7 @@ BDEPEND="virtual/pkgconfig"
 
 PATCHES=(
 	"${WORKDIR}/${PN}-patches"
+	"${FILESDIR}/${P}-clang16.patch"
 )
 
 pkg_setup() {
diff --git a/app-crypt/coolkey/files/coolkey-1.1.0-clang16.patch b/app-crypt/coolkey/files/coolkey-1.1.0-clang16.patch
new file mode 100644
index 0000000000000..88c3e11b53e8f
--- /dev/null
+++ b/app-crypt/coolkey/files/coolkey-1.1.0-clang16.patch
@@ -0,0 +1,13 @@
+Declaration taken from nss sources' lib/softoken/pkcs11i.h.
+Only needed with --enable-pk11install.
+
+https://bugs.gentoo.org/871585
+--- a/src/install/pk11install.c
++++ b/src/install/pk11install.c
+@@ -23,4 +23,6 @@
+ #include "pkcs11n.h"
+ 
++char **NSC_ModuleDBFunc(unsigned long function, char *parameters, void *args);
++
+ /*
+  * windows specific globing search