diff --git a/whalesong/js-assembler/assemble.rkt b/whalesong/js-assembler/assemble.rkt
index 1dd73a8..37d7273 100644
--- a/whalesong/js-assembler/assemble.rkt
+++ b/whalesong/js-assembler/assemble.rkt
@@ -68,7 +68,7 @@
     (display "M.params.currentSuccessHandler = success;\n" op)
     (display  #<<EOF
 for (param in params) {
-    if (params.hasOwnProperty(param)) {
+    if (Object.hasOwnProperty.call(params, param)) {
         M.params[param] = params[param];
     }
 }
diff --git a/whalesong/js-assembler/package.rkt b/whalesong/js-assembler/package.rkt
index 47587a6..124155e 100644
--- a/whalesong/js-assembler/package.rkt
+++ b/whalesong/js-assembler/package.rkt
@@ -733,7 +733,7 @@ var invokeMainModule = function() {
             M.params.currentErrorDisplayer(
                 M, $(plt.baselib.format.toDomNode(e.stack || e)).css('color', 'red'));
 
-            if (e.hasOwnProperty('racketError') &&
+            if (Object.hasOwnProperty.call(e,'racketError') &&
                 plt.baselib.exceptions.isExn(e.racketError)) {
                 contMarkSet = plt.baselib.exceptions.exnContMarks(e.racketError);
                 contextDiv = $('<div/>');
diff --git a/whalesong/js-assembler/runtime-src/baselib-format.js b/whalesong/js-assembler/runtime-src/baselib-format.js
index f9f91d9..3ea5bf1 100644
--- a/whalesong/js-assembler/runtime-src/baselib-format.js
+++ b/whalesong/js-assembler/runtime-src/baselib-format.js
@@ -199,12 +199,13 @@
     
 
 
+    var hasOwnProperty = {}.hasOwnProperty;
 
     var ToDomNodeParameters = function(params) {
         if (! params) { params = {}; }
         var k;
         for (k in params) {
-            if (params.hasOwnProperty(k)) {
+            if (hasOwnProperty.call(params, k)) {
                 this[k] = params[k];
             }
         }
diff --git a/whalesong/js-assembler/runtime-src/baselib-keywords.js b/whalesong/js-assembler/runtime-src/baselib-keywords.js
index 0e70644..02a1792 100644
--- a/whalesong/js-assembler/runtime-src/baselib-keywords.js
+++ b/whalesong/js-assembler/runtime-src/baselib-keywords.js
@@ -13,11 +13,13 @@
     };
 
     var keywordCache = {};
+
+    var hasOwnProperty = {}.hasOwnProperty;
     
     // makeInstance: string -> Keyword.
     Keyword.makeInstance = function (val) {
         // To ensure that we can eq? symbols with equal values.
-        if (!(keywordCache.hasOwnProperty(val))) {
+        if (!(hasOwnProperty.call(keywordCache, val))) {
             keywordCache[val] = new Keyword(val);
         }
         return keywordCache[val];
diff --git a/whalesong/js-assembler/runtime-src/baselib-modules.js b/whalesong/js-assembler/runtime-src/baselib-modules.js
index fa3e57b..92f1045 100644
--- a/whalesong/js-assembler/runtime-src/baselib-modules.js
+++ b/whalesong/js-assembler/runtime-src/baselib-modules.js
@@ -7,6 +7,8 @@
     var exports = {};
     baselib.modules = exports;
 
+    var hasOwnProperty = {}.hasOwnProperty;
+
     var Namespace = function(modrec) {
         this.modrec = modrec;
 
@@ -20,7 +22,7 @@
     };
 
     Namespace.prototype.hasKey = function(name) {
-        return this.mapping.hasOwnProperty(name);
+        return hasOwnProperty.call(this.mapping, name);
     };
 
     Namespace.prototype.set = function(name, value) {
diff --git a/whalesong/js-assembler/runtime-src/baselib-numbers.js b/whalesong/js-assembler/runtime-src/baselib-numbers.js
index 924f8fc..b77fede 100644
--- a/whalesong/js-assembler/runtime-src/baselib-numbers.js
+++ b/whalesong/js-assembler/runtime-src/baselib-numbers.js
@@ -69,10 +69,12 @@
     // Exports
 
 
+    var hasOwnProperty = {}.hasOwnProperty;
+
     // We first re-export everything in jsnums.
     var prop;
     for (prop in jsnums) {
-        if (jsnums.hasOwnProperty(prop)) {
+        if (hasOwnProperty.call(jsnums,prop)) {
             exports[prop] = jsnums[prop];
         }
     }
diff --git a/whalesong/js-assembler/runtime-src/baselib-symbols.js b/whalesong/js-assembler/runtime-src/baselib-symbols.js
index b7f7a42..84229a0 100644
--- a/whalesong/js-assembler/runtime-src/baselib-symbols.js
+++ b/whalesong/js-assembler/runtime-src/baselib-symbols.js
@@ -16,12 +16,14 @@
     };
 
     var symbolCache = {};
+
+    var hasOwnProperty = {}.hasOwnProperty;
     
     // makeSymbol: string -> Symbol.
     // Interns a symbol.
     var makeSymbol = function (val) {
         // To ensure that we can eq? symbols with equal values.
-        if (!(symbolCache.hasOwnProperty(val))) {
+        if (!(hasOwnProperty.call(symbolCache,val))) {
             symbolCache[val] = new Symbol(val);
         }
         return symbolCache[val];
diff --git a/whalesong/js-assembler/runtime-src/baselib.js b/whalesong/js-assembler/runtime-src/baselib.js
index 0114034..365070d 100644
--- a/whalesong/js-assembler/runtime-src/baselib.js
+++ b/whalesong/js-assembler/runtime-src/baselib.js
@@ -20,6 +20,8 @@ if (!(this.plt)) { this.plt = {}; }
 
 
 
+    var hasOwnProperty = {}.hasOwnProperty;
+
     // clone: object -> object
     // Copies an object.  The new object should respond like the old
     // object, including to things like instanceof.
@@ -29,7 +31,7 @@ if (!(this.plt)) { this.plt = {}; }
         C.prototype = obj;
         var c = new C();
         for (property in obj) {
-            if (obj.hasOwnProperty(property)) {
+            if (hasOwnProperty.call(obj, property)) {
                 c[property] = obj[property];
             }
         }