diff --git a/src/net/net.go b/src/net/net.go
index 3b37b33..27e9ca3 100644
--- a/src/net/net.go
+++ b/src/net/net.go
@@ -79,6 +79,7 @@
 package net
 
 import (
+	"context"
 	"errors"
 	"io"
 	"os"
@@ -377,6 +378,22 @@
 	ErrWriteToConnected       = errors.New("use of WriteTo with pre-connected connection")
 )
 
+// mapErr maps from the context errors to the historical internal net
+// error values.
+//
+// TODO(bradfitz): get rid of this after adjusting tests and making
+// context.DeadlineExceeded implement net.Error?
+func mapErr(err error) error {
+	switch err {
+	case context.Canceled:
+		return errCanceled
+	case context.DeadlineExceeded:
+		return errTimeout
+	default:
+		return err
+	}
+}
+
 // OpError is the error type usually returned by functions in the net
 // package. It describes the operation, network type, and address of
 // an error.