diff --git a/js/narcissus/jsdefs.js b/js/narcissus/jsdefs.js
index 4538672dc66e..a20b6d6de068 100644
--- a/js/narcissus/jsdefs.js
+++ b/js/narcissus/jsdefs.js
@@ -44,10 +44,36 @@
  * done by SpiderMonkey.
  */
 
-Narcissus = {
-    options: { version: 185 },
-    hostGlobal: this
-};
+(function() {
+    var builderTypes = Object.create(null, {
+        "default": { value: function() {
+            return new narcissus.parser.DefaultBuilder;
+        } },
+        "ssa": { value: function() {
+            return new narcissus.parser.SSABuilder;
+        } }
+    });
+
+    var builderType;
+
+    var narcissus = {
+        options: {
+            version: 185,
+            get builderType() { return builderType },
+            set builderType(type) {
+                var ctor = builderTypes[type];
+
+                if (!ctor)
+                    throw new Error("expected builder type ('default' or 'ssa'), got " + type);
+
+                builderType = type;
+                narcissus.definitions.Builder = ctor;
+            }
+        },
+        hostGlobal: this
+    };
+    Narcissus = narcissus;
+})();
 
 Narcissus.definitions = (function() {
 
@@ -270,7 +296,11 @@ Narcissus.definitions = (function() {
         defineGetter: defineGetter,
         defineProperty: defineProperty,
         isNativeCode: isNativeCode,
-        makePassthruHandler: makePassthruHandler
+        makePassthruHandler: makePassthruHandler,
+        Builder: function() {
+            throw new Error("no Builder type selected");
+        }
     };
 }());
 
+Narcissus.options.builderType = "default";
diff --git a/js/narcissus/jsexec.js b/js/narcissus/jsexec.js
index 0ab9b233f420..50dcb9033e6b 100644
--- a/js/narcissus/jsexec.js
+++ b/js/narcissus/jsexec.js
@@ -85,7 +85,7 @@ Narcissus.interpreter = (function() {
             x2.callee = x.callee;
             x2.scope = x.scope;
             try {
-                x2.execute(parser.parse(new parser.DefaultBuilder, s));
+                x2.execute(parser.parse(new definitions.Builder, s));
                 return x2.result;
             } catch (e if e instanceof SyntaxError || isStackOverflow(e)) {
                 /*
@@ -119,7 +119,7 @@ Narcissus.interpreter = (function() {
 
             // NB: Use the STATEMENT_FORM constant since we don't want to push this
             // function onto the fake compilation context.
-            var x = { builder: new parser.DefaultBuilder };
+            var x = { builder: new definitions.Builder };
             var f = parser.FunctionDefinition(t, x, false, parser.STATEMENT_FORM);
             var s = {object: global, parent: null};
             return newFunction(f,{scope:s});
@@ -1023,7 +1023,7 @@ Narcissus.interpreter = (function() {
             return s;
 
         var x = new ExecutionContext(GLOBAL_CODE);
-        x.execute(parser.parse(new parser.DefaultBuilder, s, f, l));
+        x.execute(parser.parse(new definitions.Builder, s, f, l));
         return x.result;
     }
 
@@ -1059,7 +1059,7 @@ Narcissus.interpreter = (function() {
             }
         }
 
-        var b = new parser.DefaultBuilder;
+        var b = new definitions.Builder;
         var x = new ExecutionContext(GLOBAL_CODE);
 
         ExecutionContext.current = x;
diff --git a/js/narcissus/jsparse.js b/js/narcissus/jsparse.js
index 17eb8effdbd4..6ac2586595cf 100644
--- a/js/narcissus/jsparse.js
+++ b/js/narcissus/jsparse.js
@@ -2328,6 +2328,9 @@ Narcissus.parser = (function() {
         parse: parse,
         Node: Node,
         DefaultBuilder: DefaultBuilder,
+        get SSABuilder() {
+            throw new Error("SSA builder not yet supported");
+        },
         bindSubBuilders: bindSubBuilders,
         DECLARED_FORM: DECLARED_FORM,
         EXPRESSED_FORM: EXPRESSED_FORM,
diff --git a/js/src/shell/njs b/js/src/shell/njs
index 9f11a8bc21c6..72322629c60a 100755
--- a/js/src/shell/njs
+++ b/js/src/shell/njs
@@ -35,13 +35,18 @@ if __name__ == '__main__':
             help='enable interactive shell')
     op.add_option('-H', '--harmony', dest='js_harmony', action='store_true',
             help='enable ECMAScript Harmony mode')
+    op.add_option('-S', '--ssa', dest='js_ssa', action='store_true',
+            help='enable parse-time SSA construction')
 
     (options, args) = op.parse_args()
 
     cmd = ""
 
     if options.js_harmony:
-        cmd += 'Narcissus.options={version:"harmony"}; '
+        cmd += 'Narcissus.options.version = "harmony"; '
+
+    if options.js_ssa:
+        cmd += 'Narcissus.options.builderType = "ssa"; '
 
     if options.js_exps:
         for exp in options.js_exps: