diff -ur postgresql-16.1.orig/src/bin/pg_upgrade/option.c postgresql-16.1/src/bin/pg_upgrade/option.c
--- postgresql-16.1.orig/src/bin/pg_upgrade/option.c	2023-11-06 23:04:27.000000000 +0100
+++ postgresql-16.1/src/bin/pg_upgrade/option.c	2023-12-13 21:51:21.445407619 +0100
@@ -456,8 +456,14 @@
 get_sock_dir(ClusterInfo *cluster, bool live_check)
 {
 #if !defined(WIN32)
-	if (!live_check)
+	if (!live_check) {
 		cluster->sockdir = user_opts.socketdir;
+#ifndef UNIX_PATH_MAX
+#define UNIX_PATH_MAX 108
+#endif
+		if (strlen(cluster->sockdir) >= UNIX_PATH_MAX - sizeof(".s.PGSQL.50432"))
+			strcpy(cluster->sockdir, "/tmp"); /* fall back to tmp */
+	}
 	else
 	{
 		/*
diff -ur postgresql-16.1.orig/src/include/pg_config_manual.h postgresql-16.1/src/include/pg_config_manual.h
--- postgresql-16.1.orig/src/include/pg_config_manual.h	2023-11-06 23:04:27.000000000 +0100
+++ postgresql-16.1/src/include/pg_config_manual.h	2023-12-13 21:49:50.563249439 +0100
@@ -206,7 +206,7 @@
  * support them yet.
  */
 #ifndef WIN32
-#define DEFAULT_PGSOCKET_DIR  "/tmp"
+#define DEFAULT_PGSOCKET_DIR  "/var/run/postgresql"
 #else
 #define DEFAULT_PGSOCKET_DIR ""
 #endif