diff --git a/src/bin/pg_upgrade/dump.c b/src/bin/pg_upgrade/dump.c
index 29b9e44f782..f7d6a537b4f 100644
--- a/src/bin/pg_upgrade/dump.c
+++ b/src/bin/pg_upgrade/dump.c
@@ -21,9 +21,10 @@ generate_old_dump(void)
 
 	/* run new pg_dumpall binary for globals */
 	exec_prog(UTILITY_LOG_FILE, NULL, true, true,
-			  "\"%s/pg_dumpall\" %s --globals-only --quote-all-identifiers "
+			  "\"%s/pg_dumpall\" %s%s --globals-only --quote-all-identifiers "
 			  "--binary-upgrade %s -f \"%s/%s\"",
 			  new_cluster.bindir, cluster_conn_opts(&old_cluster),
+			  protocol_negotiation_supported(&old_cluster) ? "" : " -d \"max_protocol_version=3.0\"",
 			  log_opts.verbose ? "--verbose" : "",
 			  log_opts.dumpdir,
 			  GLOBALS_DUMP_FILE);
@@ -43,6 +44,9 @@ generate_old_dump(void)
 		initPQExpBuffer(&connstr);
 		appendPQExpBufferStr(&connstr, "dbname=");
 		appendConnStrVal(&connstr, old_db->db_name);
+		if (!protocol_negotiation_supported(&old_cluster))
+			appendPQExpBufferStr(&connstr, " max_protocol_version=3.0");
+
 		initPQExpBuffer(&escaped_connstr);
 		appendShellString(&escaped_connstr, connstr.data);
 		termPQExpBuffer(&connstr);
diff --git a/src/bin/pg_upgrade/pg_upgrade.h b/src/bin/pg_upgrade/pg_upgrade.h
index 19ca68ed619..803acc696ef 100644
--- a/src/bin/pg_upgrade/pg_upgrade.h
+++ b/src/bin/pg_upgrade/pg_upgrade.h
@@ -449,6 +449,7 @@ bool		check_for_data_types_usage(ClusterInfo *cluster,
 bool		check_for_data_type_usage(ClusterInfo *cluster,
 									  const char *type_name,
 									  const char *output_path);
+bool		protocol_negotiation_supported(const ClusterInfo *cluster);
 void		old_9_3_check_for_line_data_type_usage(ClusterInfo *cluster);
 void		old_9_6_check_for_unknown_data_type_usage(ClusterInfo *cluster);
 void		old_9_6_invalidate_hash_indexes(ClusterInfo *cluster,
diff --git a/src/bin/pg_upgrade/server.c b/src/bin/pg_upgrade/server.c
index 265137e86bf..df165efac40 100644
--- a/src/bin/pg_upgrade/server.c
+++ b/src/bin/pg_upgrade/server.c
@@ -71,6 +71,8 @@ get_db_conn(ClusterInfo *cluster, const char *db_name)
 		appendPQExpBufferStr(&conn_opts, " host=");
 		appendConnStrVal(&conn_opts, cluster->sockdir);
 	}
+	if (!protocol_negotiation_supported(cluster))
+		appendPQExpBufferStr(&conn_opts, " max_protocol_version=3.0");
 
 	conn = PQconnectdb(conn_opts.data);
 	termPQExpBuffer(&conn_opts);
diff --git a/src/bin/pg_upgrade/version.c b/src/bin/pg_upgrade/version.c
index 20c61072a42..8658436b366 100644
--- a/src/bin/pg_upgrade/version.c
+++ b/src/bin/pg_upgrade/version.c
@@ -241,6 +241,37 @@ old_9_6_check_for_unknown_data_type_usage(ClusterInfo *cluster)
 		check_ok();
 }
 
+/*
+ * Older servers can't support newer protocol versions, so their connection
+ * strings will need to lock max_protocol_version to 3.0.
+ */
+bool
+protocol_negotiation_supported(const ClusterInfo *cluster)
+{
+	/*
+	 * Back-branch-specific complication: in libpq versions prior to PG18,
+	 * max_protocol_version isn't supported. But we also don't need to worry
+	 * about newer protocol versions being used in that case, so just lie and
+	 * return true.
+	 *
+	 * (Checking for a libpq version that's newer than this branch looks very
+	 * strange, but distributions are allowed to link older pg_upgrade
+	 * binaries against the newest release of libpq.)
+	 */
+	if (PQlibVersion() < 180000)
+		return true;
+
+	/*
+	 * The February 2018 patch release (9.3.21, 9.4.16, 9.5.11, 9.6.7, and
+	 * 10.2) added support for NegotiateProtocolVersion. But ClusterInfo only
+	 * has information about the major version number. To ensure we can still
+	 * upgrade older unpatched servers, just assume anything prior to PG11
+	 * can't negotiate. It's not possible for those servers to make use of
+	 * newer protocols anyway, so nothing is lost.
+	 */
+	return (GET_MAJOR_VERSION(cluster->major_version) >= 1100);
+}
+
 /*
  * old_9_6_invalidate_hash_indexes()
  *	9.6 -> 10