diff --git a/antlr-2.7.7-configure-c99.patch b/antlr-2.7.7-configure-c99.patch
new file mode 100644
index 0000000..38b83bc
--- /dev/null
+++ b/antlr-2.7.7-configure-c99.patch
@@ -0,0 +1,13 @@
+--- configure
++++ configure
+@@ -4697,8 +4697,8 @@ main ()
+   for (i = 0; i < 256; i++)
+     if (XOR (islower (i), ISLOWER (i))
+ 	|| toupper (i) != TOUPPER (i))
+-      exit(2);
+-  exit (0);
++      return 2;
++  return 0;
+ }
+ _ACEOF
+ rm -f conftest$ac_exeext
diff --git a/antlr.spec b/antlr.spec
index 8a5cf5f..c9f7f94 100644
--- a/antlr.spec
+++ b/antlr.spec
@@ -4,7 +4,7 @@
 Summary:       ANother Tool for Language Recognition
 Name:          antlr
 Version:       2.7.7
-Release:       70%{?dist}
+Release:       71%{?dist}
 License:       ANTLR-PD
 URL:           http://www.antlr2.org/
 ExclusiveArch: %{java_arches}
@@ -17,6 +17,7 @@ Source3:       http://repo2.maven.org/maven2/antlr/antlr/%{version}/%{name}-%{ve
 # Repack the tarball without prebuilt binaries of unknown origin
 Source4:       generate-tarball.sh
 Patch1:        %{name}-%{version}-newgcc.patch
+Patch2:        %{name}-%{version}-configure-c99.patch
 
 BuildRequires: gcc-c++
 BuildRequires: make
@@ -73,6 +74,7 @@ This package provides a static C++ library for parsers generated by ANTLR2.
 find . -name "*.jar" -exec rm -f {} \;
 cp -p %{SOURCE1} build.xml
 %patch1
+%patch2
 # CRLF->LF
 sed -i 's/\r//' LICENSE.txt
 
@@ -129,6 +131,9 @@ install -p -m 755 scripts/antlr-config $RPM_BUILD_ROOT%{_bindir}
 %license LICENSE.txt
 
 %changelog
+* Tue Dec 06 2022 Peter Fordham <peter.fordham@gmail.com> - 2.7.7-71
+- Port configure script to C99.
+
 * Wed Jul 20 2022 Fedora Release Engineering <releng@fedoraproject.org> - 2.7.7-70
 - Rebuilt for https://fedoraproject.org/wiki/Fedora_37_Mass_Rebuild