diff --git a/js/client/modules/@arangodb/testing.js b/js/client/modules/@arangodb/testing.js
index c61740d02c..00ff1d6253 100644
--- a/js/client/modules/@arangodb/testing.js
+++ b/js/client/modules/@arangodb/testing.js
@@ -1464,7 +1464,7 @@ function startInstanceAgency (instanceInfo, protocol, options,
 
   for (let i = 0; i < N; i++) {
     let instanceArgs = _.clone(addArgs);
-    instanceArgs['log.file'] = "log" + String(i);
+    instanceArgs['log.file'] = fs.join(rootDir, 'log' + String(i));
     instanceArgs['agency.activate'] = 'true';
     instanceArgs['agency.size'] = String(N);
     instanceArgs['agency.pool-size'] = String(N);