diff --git a/misc/cgo/test/issue4339.go b/misc/cgo/test/issue4339.go
index 4fa4b2bbd7..3715fde575 100644
--- a/misc/cgo/test/issue4339.go
+++ b/misc/cgo/test/issue4339.go
@@ -5,7 +5,8 @@
 package cgotest
 
 /*
-#include "issue4339.h"
+// We've historically permitted #include <>, so test it here.  Issue 29333.
+#include <issue4339.h>
 */
 import "C"
 
diff --git a/src/cmd/cgo/gcc.go b/src/cmd/cgo/gcc.go
index 27bd59b54e..11c3ff3a9c 100644
--- a/src/cmd/cgo/gcc.go
+++ b/src/cmd/cgo/gcc.go
@@ -1992,8 +1992,10 @@ func (p *Package) gccErrors(stdin []byte) string {
 		}
 	}
 
-	// Force -O0 optimization
+	// Force -O0 optimization but keep the trailing "-" at the end.
 	nargs = append(nargs, "-O0")
+	nl := len(nargs)
+	nargs[nl-2], nargs[nl-1] = nargs[nl-1], nargs[nl-2]
 
 	if *debugGcc {
 		fmt.Fprintf(os.Stderr, "$ %s <<EOF\n", strings.Join(nargs, " "))