diff --git a/artiq/coredevice/exceptions.py b/artiq/coredevice/exceptions.py
index 1669c6096..b1ba94ff3 100644
--- a/artiq/coredevice/exceptions.py
+++ b/artiq/coredevice/exceptions.py
@@ -135,4 +135,4 @@ class WatchdogExpired(Exception):
     """Raised when a watchdog expires."""
 
 class ClockFailure(Exception):
-    """Raised when RTIO PLL is unable to lock."""
+    """Raised when RTIO PLL has lost lock."""