diff --git a/bar.go b/bar.go
index 92ef92c..ab56127 100644
--- a/bar.go
+++ b/bar.go
@@ -161,7 +161,7 @@
 // ProxyReader wraps r with metrics required for progress tracking.
 func (b *Bar) ProxyReader(r io.Reader) io.ReadCloser {
 	if r == nil {
-		panic("expect io.Reader, got nil")
+		return nil
 	}
 	rc, ok := r.(io.ReadCloser)
 	if !ok {