diff --git a/src/cmd/asm/main.go b/src/cmd/asm/main.go
index 92428fc811..13e5302301 100644
--- a/src/cmd/asm/main.go
+++ b/src/cmd/asm/main.go
@@ -80,6 +80,7 @@ func main() {
 		} else {
 			log.Print("assembly failed")
 		}
+		out.Close()
 		os.Remove(*flags.OutputFile)
 		os.Exit(1)
 	}