diff --git a/src/runtime/time.go b/src/runtime/time.go
index ffe7590526..3f8f6968c2 100644
--- a/src/runtime/time.go
+++ b/src/runtime/time.go
@@ -16,7 +16,7 @@ type timer struct {
 	i int // heap index
 
 	// Timer wakes up at when, and then at when+period, ... (period > 0 only)
-	// each time calling f(now, arg) in the timer goroutine, so f must be
+	// each time calling f(arg, now) in the timer goroutine, so f must be
 	// a well-behaved function and not block.
 	when   int64
 	period int64