src/cmd/cgo/ast.go | 4 ++++

diff --git a/src/cmd/cgo/ast.go b/src/cmd/cgo/ast.go
index 7c64a5d246c9a149072d99bdd94cb610f5e6efd7..8689ac3dac2510293a975dfbf5422d7701325cb3 100644
--- a/src/cmd/cgo/ast.go
+++ b/src/cmd/cgo/ast.go
@@ -141,6 +141,10 @@ 			if context == "as2" {
 				context = "expr"
 			}
 			goname := sel.Sel.Name
+			if goname == "errno" {
+				error(sel.Pos(), "cannot refer to errno directly; see documentation")
+				return
+			}
 			name := f.Name[goname]
 			if name == nil {
 				name = &Name{