diff --git a/prometheus/metric.go b/prometheus/metric.go
index f018e57..07bbc9d 100644
--- a/prometheus/metric.go
+++ b/prometheus/metric.go
@@ -92,9 +92,6 @@ type Opts struct {
 	// machine_role metric). See also
 	// https://prometheus.io/docs/instrumenting/writing_exporters/#target-labels-not-static-scraped-labels
 	ConstLabels Labels
-
-	// now is for testing purposes, by default it's time.Now.
-	now func() time.Time
 }
 
 // BuildFQName joins the given three name components by "_". Empty name