diff --git a/prometheus/registry.go b/prometheus/registry.go
index 8485f9a..81eda27 100644
--- a/prometheus/registry.go
+++ b/prometheus/registry.go
@@ -427,7 +427,7 @@ func (r *registry) writePB(w io.Writer, writeEncoded encoder) (int, error) {
 
 	// Drain metricChan in case of premature return.
 	defer func() {
-		for range metricChan {
+		for _ = range metricChan {
 		}
 	}()