diff --git a/t/web-lib-funcs-miniserv-config.t b/t/web-lib-funcs-miniserv-config.t
new file mode 100644
index 000000000..5c9765334
--- /dev/null
+++ b/t/web-lib-funcs-miniserv-config.t
@@ -0,0 +1,49 @@
+#!/usr/bin/perl
+# Concurrent WebSocket updates must not reuse a same-second config snapshot.
+use strict;
+use warnings;
+use Test::More;
+use File::Temp qw(tempdir);
+use File::Basename qw(dirname);
+use File::Spec;
+
+require File::Spec->rel2abs(dirname(__FILE__).'/../web-lib-funcs.pl');
+my $directory = tempdir(CLEANUP => 1);
+my $file = "$directory/miniserv.conf";
+{
+	no warnings qw(redefine once);
+	*main::get_miniserv_config_file = sub { return $file; };
+}
+
+# replace_config(contents) simulates another process writing within one second.
+sub replace_config
+{
+my ($contents) = @_;
+open(my $fh, '>', $file) or die $!;
+print {$fh} $contents;
+close($fh) or die $!;
+utime(1700000000, 1700000000, $file) or die $!;
+}
+
+replace_config("port=10000\nwebsockets_/test/ws-555=first\n");
+my %first;
+ok(main::get_miniserv_config(\%first), 'read initial configuration');
+is($first{'websockets_/test/ws-555'}, 'first', 'first route is present');
+
+# Allocation must retain a route added since the caller's initial config read.
+replace_config("port=10000\nwebsockets_/test/ws-555=first\n".
+	"websockets_/test/ws-556=second\n");
+my %added;
+main::get_miniserv_config(\%added);
+is($added{'websockets_/test/ws-556'}, 'second',
+	'same-second route addition is visible');
+
+# Cleanup must not restore a route another backend has already removed.
+replace_config("port=10000\nwebsockets_/test/ws-556=second\n");
+my %removed;
+main::get_miniserv_config(\%removed);
+ok(!exists($removed{'websockets_/test/ws-555'}),
+	'same-second route removal is visible');
+is($removed{'websockets_/test/ws-556'}, 'second',
+	'unrelated route survives cleanup');
+done_testing();
diff --git a/web-lib-funcs.pl b/web-lib-funcs.pl
index e32e3399a..eb63e8e00 100755
--- a/web-lib-funcs.pl
+++ b/web-lib-funcs.pl
@@ -3083,7 +3083,9 @@ hash reference.
 =cut
 sub get_miniserv_config
 {
-return &read_file_cached_with_stat(&get_miniserv_config_file(), $_[0]);
+# WebSocket backends can change routes several times within one second.
+# An mtime-based cache can lose another process's update even under a file lock.
+return &read_file(&get_miniserv_config_file(), $_[0]);
 }
 
 =head2 put_miniserv_config(&hash)