diff --git a/ChangeLog b/ChangeLog
index aad5700a8..89e13873f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+2022-11-25  Florian Weimer
+
+	* config/config.poll-dev.c:
+	* config/config.proccmd.c:
+	* config/config.reuseaddr.c:
+	* config/config.vasprintf.c:
+	* config/config.vsprintf.c:
+	Make config tests work with C99 compiler
+
 2022-11-21  Wolfgang Lux  <wolfgang.lux@gmail.com>
 
 	* Source/NSFileManager.m:
diff --git a/config/config.poll-dev.c b/config/config.poll-dev.c
index 413a6a7ad..ec3238740 100644
--- a/config/config.poll-dev.c
+++ b/config/config.poll-dev.c
@@ -6,6 +6,7 @@
 #include <stdio.h>
 #include <fcntl.h>
 #include <poll.h>
+#include <unistd.h>
 
 int
 main()
diff --git a/config/config.proccmd.c b/config/config.proccmd.c
index b27d25a56..3e5a5a387 100644
--- a/config/config.proccmd.c
+++ b/config/config.proccmd.c
@@ -10,6 +10,8 @@
   notice and this notice are preserved.
 */
 #include <stdio.h>
+#include <unistd.h>
+
 int main()
 {
   char	buf[32];
diff --git a/config/config.reuseaddr.c b/config/config.reuseaddr.c
index 45276c8cd..6061b7814 100644
--- a/config/config.reuseaddr.c
+++ b/config/config.reuseaddr.c
@@ -31,7 +31,7 @@
 // Maximum data in single I/O operation
 #define	NETBUF_SIZE	4096
 
-main()
+int main()
 {
   struct sockaddr_in	sin;
   int	size = sizeof(sin);
diff --git a/config/config.vasprintf.c b/config/config.vasprintf.c
index a3c755ec9..f532502e1 100644
--- a/config/config.vasprintf.c
+++ b/config/config.vasprintf.c
@@ -25,6 +25,6 @@ static int func(const char *fmt, ...)
 int main()
 {
   if (func("1234", 0) == 4)
-    exit (0);
-  exit (-1);
+    return 0;
+  return -1;
 }
diff --git a/config/config.vsprintf.c b/config/config.vsprintf.c
index 01a383d61..a4a971e80 100644
--- a/config/config.vsprintf.c
+++ b/config/config.vsprintf.c
@@ -25,6 +25,6 @@ static int func(const char *fmt, ...)
 int main()
 {
   if (func("1234", 0) == 4)
-    exit (0);
-  exit (-1);
+    return 0;
+  return -1;
 }