diff --git a/qa/qa_instance.py b/qa/qa_instance.py
index c1d660f11b8327314aa6be54bb06f6216f015075..72b69de2628bceb806b81e18700f351690ceda0b 100644
--- a/qa/qa_instance.py
+++ b/qa/qa_instance.py
@@ -215,7 +215,8 @@ def TestInstanceConvertDisk(instance, snode):
   cmd = ['gnt-instance', 'modify', '-t', 'plain', instance['name']]
   AssertEqual(StartSSH(master['primary'],
                        utils.ShellQuoteArgs(cmd)).wait(), 0)
-  cmd = ['gnt-instance', 'modify', '-t', 'drbd', '-n', snode, instance['name']]
+  cmd = ['gnt-instance', 'modify', '-t', 'drbd', '-n', snode['primary'],
+         instance['name']]
   AssertEqual(StartSSH(master['primary'],
                        utils.ShellQuoteArgs(cmd)).wait(), 0)