diff --git a/src/runtime/mgc.go b/src/runtime/mgc.go
index 54fc6a6e282..7c7239beb8d 100644
--- a/src/runtime/mgc.go
+++ b/src/runtime/mgc.go
@@ -302,8 +302,8 @@ const (
 	// gcMarkWorkerFractionalMode indicates that a P is currently
 	// running the "fractional" mark worker. The fractional worker
 	// is necessary when GOMAXPROCS*gcBackgroundUtilization is not
-	// an integer and the utilization too far away from the
-	// gcBackgroundUtilization when round the number.
+	// an integer and using only dedicated workers would result in
+	// utilization too far from the target of gcBackgroundUtilization.
 	// The fractional worker should run until it is preempted and
 	// will be scheduled to pick up the fractional part of
 	// GOMAXPROCS*gcBackgroundUtilization.