diff --git a/scripts/build-remote.pl.in b/scripts/build-remote.pl.in
index 8bf77df04b..fca00241bf 100755
--- a/scripts/build-remote.pl.in
+++ b/scripts/build-remote.pl.in
@@ -232,10 +232,24 @@ sub removeRoots {
 # the same missing path simultaneously, causing the effective network
 # bandwidth and target disk speed to be divided by N.
 my $uploadLock = "$currentLoad/$hostName.upload-lock";
-sysopen MAINLOCK, "$uploadLock", O_RDWR|O_CREAT, 0600 or die;
-flock(MAINLOCK, LOCK_EX) or die;
+sysopen UPLOADLOCK, "$uploadLock", O_RDWR|O_CREAT, 0600 or die;
+eval {
+    local $SIG{ALRM} = sub { die "alarm\n" };
+    # Don't wait forever, so that a process that gets stuck while
+    # holding the lock doesn't block everybody else indefinitely.
+    # It's safe to continue after a timeout, just (potentially)
+    # inefficient.
+    alarm 15 * 60;
+    flock(UPLOADLOCK, LOCK_EX);
+    alarm 0;
+};
+if ($@) {
+    die unless $@ eq "alarm\n";
+    print STDERR "somebody is hogging $uploadLock, continuing...\n";
+    unlink $uploadLock;
+}
 Nix::CopyClosure::copyTo($hostName, [ @sshOpts ], [ $drvPath, @inputs ], "", "", 0, 0, $maybeSign ne "");
-close MAINLOCK;
+close UPLOADLOCK;
 
 
 # Perform the build.