diff --git a/whalesong/js-assembler/assemble.rkt b/whalesong/js-assembler/assemble.rkt
index e4e779f..1dd73a8 100644
--- a/whalesong/js-assembler/assemble.rkt
+++ b/whalesong/js-assembler/assemble.rkt
@@ -39,6 +39,7 @@
   (parameterize ([current-interned-symbol-table ((inst make-hash Symbol Symbol))]
                  [current-interned-constant-closure-table ((inst make-hash Symbol MakeCompiledProcedure))])
     (display "(function(M, success, fail, params) {\n" op)
+    (display "\"use strict\";\n" op)
     (display "var param;\n" op)
     (display "var RT = plt.runtime;\n" op)
     
diff --git a/whalesong/js-assembler/package.rkt b/whalesong/js-assembler/package.rkt
index 3edf552..47587a6 100644
--- a/whalesong/js-assembler/package.rkt
+++ b/whalesong/js-assembler/package.rkt
@@ -393,7 +393,7 @@ M.modules[~s] =
        (define start-time (current-inexact-milliseconds))
        (cond
         [(UninterpretedSource? src)
-         (fprintf op "(function(M) { ~a }(plt.runtime.currentMachine));" (UninterpretedSource-datum src))]
+         (fprintf op "(function(M) {\n\"use strict\";\n ~a }(plt.runtime.currentMachine));" (UninterpretedSource-datum src))]
         [else      
          (fprintf op "(")
          (on-source src stmts op)