diff --git a/sink.go b/sink.go
index df46fa87a..f45080a2c 100644
--- a/sink.go
+++ b/sink.go
@@ -32,7 +32,7 @@ import (
 	"go.uber.org/zap/zapcore"
 )
 
-const schemeFile = "file"
+const _schemeFile = "file"
 
 var (
 	_sinkMutex     sync.RWMutex
@@ -48,7 +48,7 @@ func resetSinkRegistry() {
 	defer _sinkMutex.Unlock()
 
 	_sinkFactories = map[string]func(*url.URL) (Sink, error){
-		schemeFile: newFileSink,
+		_schemeFile: newFileSink,
 	}
 }
 
@@ -101,7 +101,7 @@ func newSink(rawURL string) (Sink, error) {
 		return nil, fmt.Errorf("can't parse %q as a URL: %v", rawURL, err)
 	}
 	if u.Scheme == "" {
-		u.Scheme = schemeFile
+		u.Scheme = _schemeFile
 	}
 
 	_sinkMutex.RLock()