diff --git a/src/BuildRunner.php b/src/BuildRunner.php
index 1bb81a3..d3bb6e1 100644
--- a/src/BuildRunner.php
+++ b/src/BuildRunner.php
@@ -142,6 +142,15 @@ YAML;
             return BuildRepository::getById($id) ?? ['id' => $id, 'build_code' => $buildCode, 'status' => 'failed'];
         }
         $logPath = $dir . '/build.log';
+        if (@file_put_contents($logPath, "[builder] Build queued\n", FILE_APPEND) === false) {
+            self::failBuild(
+                $id,
+                'Cannot write build log: ' . $logPath
+                . ' (run prepare-be-builder-dirs.sh; builds/ must be writable by PHP-FPM user nobody)',
+                null
+            );
+            return BuildRepository::getById($id) ?? ['id' => $id, 'build_code' => $buildCode, 'status' => 'failed'];
+        }
         BuildRepository::update($id, ['log_path' => $logPath]);
 
         if (!self::dockerAvailable()) {