diff --git a/prometheus/process_collector_darwin.go b/prometheus/process_collector_darwin.go
index fb73117a1..6612adc0a 100644
--- a/prometheus/process_collector_darwin.go
+++ b/prometheus/process_collector_darwin.go
@@ -25,7 +25,7 @@ import (
 
 // notImplementedErr is returned by stub functions that replace cgo functions, when cgo
 // isn't available.
-var notImplementedErr = fmt.Errorf("not implemented")
+var notImplementedErr = errors.New("not implemented")
 
 type memoryInfo struct {
 	vsize uint64 // Virtual memory size in bytes