diff --git a/autogen-configure-c99.patch b/autogen-configure-c99.patch
new file mode 100644
index 0000000..136500c
--- /dev/null
+++ b/autogen-configure-c99.patch
@@ -0,0 +1,44 @@
+diff --git a/config/ag_macros.m4 b/config/ag_macros.m4
+index ccce347..ae36cf7 100644
+--- a/config/ag_macros.m4
++++ b/config/ag_macros.m4
+@@ -113,7 +113,7 @@ AC_DEFUN([INVOKE_AG_MACROS_LAST],[
+   fi
+ 
+   AC_CACHE_CHECK([for static inline], [snv_cv_static_inline], [
+-  AC_TRY_COMPILE([static inline foo(bar) int bar; { return bar; }],
++  AC_TRY_COMPILE([static inline int foo(bar) int bar; { return bar; }],
+     [return foo(0);],
+     [snv_cv_static_inline='static inline'],
+     [snv_cv_static_inline='static'])
+@@ -428,7 +428,7 @@ int main (int argc, char ** argv) {
+    char zRej@<:@@:>@ = reject;
+    char zAcc@<:@@:>@ = "a-ok-eject";
+    return strcspn( zAcc, zRej ) - 5;
+-}] )]
++}] )],
+     [ag_cv_run_strcspn=yes],[ag_cv_run_strcspn=no],[ag_cv_run_strcspn=no]
+   ) # end of RUN_IFELSE
+   ]) # end of AC_CACHE_VAL for ag_cv_run_strcspn
+diff --git a/configure b/configure
+index 518ac9c..5eacd76 100755
+--- a/configure
++++ b/configure
+@@ -17338,7 +17338,7 @@ int main (int argc, char ** argv) {
+    char zAcc[] = "a-ok-eject";
+    return strcspn( zAcc, zRej ) - 5;
+ }
+-    ag_cv_run_strcspn=yes
++#error
+ _ACEOF
+ if ac_fn_c_try_run "$LINENO"; then :
+   ag_cv_run_strcspn=no
+@@ -18406,7 +18405,7 @@ else
+ 
+   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+ /* end confdefs.h.  */
+-static inline foo(bar) int bar; { return bar; }
++static inline int foo(bar) int bar; { return bar; }
+ int
+ main ()
+ {
diff --git a/autogen.spec b/autogen.spec
index f95c1ef..5116c78 100644
--- a/autogen.spec
+++ b/autogen.spec
@@ -1,7 +1,7 @@
 Summary:	Automated text file generator
 Name:		autogen
 Version:	5.18.16
-Release:	11%{?dist}
+Release:	12%{?dist}
 # Some files are licensed under GPLv2+.
 # We redistribute them under GPLv3+.
 License:	GPLv3+
@@ -12,6 +12,7 @@ Source0:	ftp://ftp.gnu.org/gnu/autogen/rel%{version}/%{name}-%{version}.tar.xz
 Patch0:		autogen-multilib.patch
 # Fix gcc error on overlapping strings
 Patch1:		autogen-overlap.patch
+Patch2:		autogen-configure-c99.patch
 
 Requires:	%{name}-libopts%{?_isa} = %{version}-%{release}
 
@@ -68,6 +69,7 @@ This package contains development files for libopts.
 %setup -q
 %patch0 -p1 -b .multilib
 %patch1 -p1 -b .overlap
+%patch2 -p1
 
 # Disable failing test
 sed -i 's|errors.test||' autoopts/test/Makefile.in
@@ -144,6 +146,9 @@ rm -f $RPM_BUILD_ROOT%{_infodir}/dir
 %{_includedir}/autoopts/usage-txt.h
 
 %changelog
+* Wed Dec 07 2022 Peter Fordham <peter.fordham@gmail.com> - 5.18.16-12
+- Patch in fix for https://sourceforge.net/p/autogen/bugs/213/, C99 compliance.
+
 * Wed Jul 20 2022 Fedora Release Engineering <releng@fedoraproject.org> - 5.18.16-11
 - Rebuilt for https://fedoraproject.org/wiki/Fedora_37_Mass_Rebuild