diff --git a/src/cmd/compile/internal/base/flag.go b/src/cmd/compile/internal/base/flag.go
index 8ffb41b16d..0e44deae71 100644
--- a/src/cmd/compile/internal/base/flag.go
+++ b/src/cmd/compile/internal/base/flag.go
@@ -334,6 +334,7 @@ func ParseFlags() {
 		// It is not possible to build the runtime with no optimizations,
 		// because the compiler cannot eliminate enough write barriers.
 		Flag.N = 0
+		Ctxt.Flag_optimize = true
 
 		// Runtime can't use -d=checkptr, at least not yet.
 		Debug.Checkptr = 0