diff --git a/asm.js b/asm.js
index 3cbe273..bb03c0c 100644
--- a/asm.js
+++ b/asm.js
@@ -1306,7 +1306,7 @@ export class Assembler {
                 ...data,
             ]
         });
-        return [ contents.length ].concat(...contents);
+        return [ contents.length, contents ].flat(Infinity);
     }
 
 	wasm() {
@@ -1326,10 +1326,10 @@ export class Assembler {
         ];
         const sections = template.map(([ code, generator ]) => {
             const body = generator();
-            return body == null ? [] : [ code, body.length, ...body ];
+            return body == null ? [] : [ code, body.length, body ];
         });
 
-		return new Uint8Array(HEADER.concat(...sections));
+		return new Uint8Array([ HEADER, sections ].flat(Infinity));
 	}
 
     mem_wasm({ flags, init, max }) {