diff --git a/0020-backport-avoid-calling-functions-without-prototype.patch b/0020-backport-avoid-calling-functions-without-prototype.patch
new file mode 100644
index 0000000000000000000000000000000000000000..96e0af1e5f41efd3c997557e6fb7a07118281484
--- /dev/null
+++ b/0020-backport-avoid-calling-functions-without-prototype.patch
@@ -0,0 +1,60 @@
+From 17c6c80de8edd5d08db5bc2f914af6473a6f0f46 Mon Sep 17 00:00:00 2001
+From: yuncang123 <1050706328@qq.com>
+Date: Sun, 1 Sep 2024 16:08:07 +0800
+Subject: [PATCH] backport-pgp-avoid calling functions without prototype
+
+---
+ src/libopensc/card-openpgp.c | 12 ++++++------
+ 1 file changed, 6 insertions(+), 6 deletions(-)
+
+diff --git a/src/libopensc/card-openpgp.c b/src/libopensc/card-openpgp.c
+index fad32f0..e4e6cc4 100644
+--- a/src/libopensc/card-openpgp.c
++++ b/src/libopensc/card-openpgp.c
+@@ -129,7 +129,7 @@ static pgp_ec_curves_t	ec_curves_gnuk[] = {
+ 
+ static int		pgp_get_card_features(sc_card_t *card);
+ static int		pgp_finish(sc_card_t *card);
+-static void		pgp_iterate_blobs(pgp_blob_t *, void (*func)());
++static void		pgp_free_blobs(pgp_blob_t *);
+ 
+ static int		pgp_get_blob(sc_card_t *card, pgp_blob_t *blob,
+ 				 unsigned int id, pgp_blob_t **ret);
+@@ -947,7 +947,7 @@ pgp_finish(sc_card_t *card)
+ 
+ 		if (priv != NULL) {
+ 			/* delete fake file hierarchy */
+-			pgp_iterate_blobs(priv->mf, pgp_free_blob);
++			pgp_free_blobs(priv->mf);
+ 
+ 			/* delete private data */
+ 			free(priv);
+@@ -1147,10 +1147,10 @@ pgp_free_blob(pgp_blob_t *blob)
+ 
+ 
+ /**
+- * Internal: iterate through the blob tree, calling a function for each blob.
++ * Internal: iterate through the blob tree, calling pgp_free_blob for each blob.
+  */
+ static void
+-pgp_iterate_blobs(pgp_blob_t *blob, void (*func)())
++pgp_free_blobs(pgp_blob_t *blob)
+ {
+ 	if (blob) {
+ 		pgp_blob_t *child = blob->files;
+@@ -1158,10 +1158,10 @@ pgp_iterate_blobs(pgp_blob_t *blob, void (*func)())
+ 		while (child != NULL) {
+ 			pgp_blob_t *next = child->next;
+ 
+-			pgp_iterate_blobs(child, func);
++			pgp_free_blobs(child);
+ 			child = next;
+ 		}
+-		func(blob);
++		pgp_free_blob(blob);
+ 	}
+ }
+ 
+-- 
+2.43.0
+
diff --git a/opensc.spec b/opensc.spec
index 61d4e4ee42d0c80e0e54717da685fc14262ec682..87ef2d04693c3290b69c040446b77cd6ba934f32 100644
--- a/opensc.spec
+++ b/opensc.spec
@@ -3,7 +3,7 @@
 
 Name:            opensc
 Version:         0.23.0
-Release:         5
+Release:         6
 License:         LGPL-2.1-or-later
 Summary:         Smart card library and applications
 URL:             https://github.com/OpenSC/OpenSC/wiki
@@ -33,6 +33,7 @@ Patch17:        0018-opensc-CVE-2023-40661-12of12.patch
 # https://github.com/OpenSC/OpenSC/pull/2948
 # https://github.com/OpenSC/OpenSC/pull/3016
 Patch18:        0019-opensc-CVE-2023-5992.patch
+Patch19:        0020-backport-avoid-calling-functions-without-prototype.patch
 
 BuildRequires:   openssl-devel pcsc-lite-devel bash-completion docbook-style-xsl readline-devel
 BuildRequires:   desktop-file-utils /usr/bin/xsltproc autoconf automake libtool gcc
@@ -64,6 +65,9 @@ cp -p src/pkcs15init/README ./README.pkcs15init
 cp -p src/scconf/README.scconf .
 
 %build
+%if "%toolchain" == "clang"
+  CFLAGS="$CFLAGS -Wno-error=unused-command-line-argument -Wno-error=unused-but-set-variable"
+%endif
 autoreconf -fvi
 sed -i -e 's/opensc.conf/opensc-%{_arch}.conf/g' src/libopensc/Makefile.in
 sed -i -e 's|"/lib /usr/lib\b|"/%{_lib} %{_libdir}|' configure # lib64 rpaths
@@ -163,6 +167,9 @@ make check
 %{_datadir}/opensc/
 
 %changelog
+* Sun Sep 1 2024 yuanchao <1050706328@qq.com> - 0.23.0-6
+- backport:avoid calling functions without prototype,and add compiler flags to support clang build
+
 * Fri Jun 28 2024 dillon chen <dillon.chen@gmail.com> - 0.23.0-5
 - fix CVE-2023-5992