diff --git a/src/metrics.js b/src/metrics.js
index 786ae8aa9..309afea45 100644
--- a/src/metrics.js
+++ b/src/metrics.js
@@ -112,7 +112,7 @@ async function readDiskMetrics() {
 
     const diskstats = await fs.promises.readFile('/proc/diskstats', { encoding: 'utf8' });
     const statsLine = diskstats.split('\n').find(l => l.includes(` ${blockDevice} `));
-    if (!blockDevice) throw new BoxError(BoxError.EXTERNAL_ERROR, 'Could not get disk stats');
+    if (!statsLine) throw new BoxError(BoxError.EXTERNAL_ERROR, 'Could not get disk stats');
 
     const parts = statsLine.trim().split(/\s+/);
     const sectorsRead = parseInt(parts[5], 10);   // field 6 . one sectiro is 512 bytes