diff --git a/raptor2-configure-c99.patch b/raptor2-configure-c99.patch
new file mode 100644
index 0000000..23d9472
--- /dev/null
+++ b/raptor2-configure-c99.patch
@@ -0,0 +1,35 @@
+Include <stdio.h> for printf in __FUNCTION__ check.  Otherwise, the
+check will fail with compilers which do not implement implicit
+function declarations (a C feature that was removed in 1999 from the
+language), no matter if the compiler supports FUNCTION or not.
+
+Submitted upstream: <https://github.com/dajobe/raptor/pull/56>
+
+diff --git a/configure b/configure
+index b0091892a210361d..08501ac8ed5e4fe1 100755
+--- a/configure
++++ b/configure
+@@ -13747,6 +13747,8 @@ esac
+ $as_echo_n "checking whether __FUNCTION__ is available... " >&6; }
+ cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+ /* end confdefs.h.  */
++
++#include <stdio.h>
+ int main() { printf(__FUNCTION__); }
+ _ACEOF
+ if ac_fn_c_try_compile "$LINENO"; then :
+diff --git a/configure.ac b/configure.ac
+index 10ff870805b82e65..40a8548b6406866a 100644
+--- a/configure.ac
++++ b/configure.ac
+@@ -312,7 +312,9 @@ AC_C_BIGENDIAN
+ AC_C_INLINE
+ 
+ AC_MSG_CHECKING(whether __FUNCTION__ is available)
+-AC_COMPILE_IFELSE([AC_LANG_SOURCE([int main() { printf(__FUNCTION__); }])],
++AC_COMPILE_IFELSE([AC_LANG_SOURCE([
++#include <stdio.h>
++int main() { printf(__FUNCTION__); }])],
+     [AC_DEFINE([HAVE___FUNCTION__], [1], [Is __FUNCTION__ available])
+      AC_MSG_RESULT(yes)],
+     [AC_MSG_RESULT(no)])
diff --git a/raptor2.spec b/raptor2.spec
index 4a37434..b500e4c 100644
--- a/raptor2.spec
+++ b/raptor2.spec
@@ -2,7 +2,7 @@
 Summary: RDF Parser Toolkit for Redland
 Name:    raptor2
 Version: 2.0.15
-Release: 34%{?dist}
+Release: 35%{?dist}
 
 License: GPLv2+ or LGPLv2+ or ASL 2.0
 Source:  http://download.librdf.org/source/raptor2-%{version}.tar.gz
@@ -15,6 +15,7 @@ Patch1: 0001-Calcualte-max-nspace-declarations-correctly-for-XML-.patch
 Patch2: 0001-CVE-2020-25713-raptor2-malformed-input-file-can-lead.patch
 
 ## upstreamable patches
+Patch3: raptor2-configure-c99.patch
 
 BuildRequires: make
 BuildRequires: gcc-c++
@@ -101,6 +102,9 @@ make check
 
 
 %changelog
+* Thu Dec  8 2022 Florian Weimer <fweimer@redhat.com> - 2.0.15-35
+- Port configure script to C99
+
 * Mon Aug 01 2022 Frantisek Zatloukal <fzatlouk@redhat.com> - 2.0.15-34
 - Rebuilt for ICU 71.1