diff -ru postfix-3.6.2.orig/src/util/sys_compat.c postfix-3.6.2/src/util/sys_compat.c
--- postfix-3.6.2.orig/src/util/sys_compat.c	2021-09-15 16:42:06.337124020 +0200
+++ postfix-3.6.2/src/util/sys_compat.c	2021-09-15 16:43:00.893791647 +0200
@@ -286,7 +286,7 @@
 
 /* closefrom() - closes all file descriptors from the given one up */
 
-int     closefrom(int lowfd)
+void     closefrom(int lowfd)
 {
     int     fd_limit = open_limit(0);
     int     fd;
@@ -298,14 +298,12 @@
      */
     if (lowfd < 0) {
 	errno = EBADF;
-	return (-1);
+	return;
     }
     if (fd_limit > 500)
 	fd_limit = 500;
     for (fd = lowfd; fd < fd_limit; fd++)
 	(void) close(fd);
-
-    return (0);
 }
 
 #endif
diff -ru postfix-3.6.2.orig/src/util/sys_defs.h postfix-3.6.2/src/util/sys_defs.h
--- postfix-3.6.2.orig/src/util/sys_defs.h	2021-09-15 16:42:06.337124020 +0200
+++ postfix-3.6.2/src/util/sys_defs.h	2021-09-15 16:42:34.500457851 +0200
@@ -1509,7 +1509,7 @@
 #endif
 
 #ifndef HAS_CLOSEFROM
-extern int closefrom(int);
+extern void closefrom(int);
 
 #endif