diff --git a/js/src/jsapi.cpp b/js/src/jsapi.cpp
--- a/js/src/jsapi.cpp
+++ b/js/src/jsapi.cpp
@@ -4796,16 +4796,26 @@ JS_EvaluateScriptForPrincipals(JSContext
         return JS_FALSE;
     JSBool ok = JS_EvaluateUCScriptForPrincipals(cx, obj, principals, chars, length,
                                                  filename, lineno, rval);
     cx->free(chars);
     return ok;
 }
 
 JS_PUBLIC_API(JSBool)
+JS_EvaluateScriptForPrincipalsVersion(JSContext *cx, JSObject *obj, JSPrincipals *principals,
+                                      const char *bytes, uintN nbytes,
+                                      const char *filename, uintN lineno, jsval *rval, JSVersion version)
+{
+    AutoVersionAPI avi(cx, version);
+    return JS_EvaluateScriptForPrincipals(cx, obj, principals, bytes, nbytes, filename, lineno,
+                                          rval);
+}
+
+JS_PUBLIC_API(JSBool)
 JS_EvaluateScript(JSContext *cx, JSObject *obj, const char *bytes, uintN nbytes,
                   const char *filename, uintN lineno, jsval *rval)
 {
     return JS_EvaluateScriptForPrincipals(cx, obj, NULL, bytes, nbytes, filename, lineno, rval);
 }
 
 JS_PUBLIC_API(JSBool)
 JS_CallFunction(JSContext *cx, JSObject *obj, JSFunction *fun, uintN argc, jsval *argv,
diff --git a/js/src/jsapi.h b/js/src/jsapi.h
--- a/js/src/jsapi.h
+++ b/js/src/jsapi.h
@@ -2535,16 +2535,23 @@ JS_EvaluateScript(JSContext *cx, JSObjec
 extern JS_PUBLIC_API(JSBool)
 JS_EvaluateScriptForPrincipals(JSContext *cx, JSObject *obj,
                                JSPrincipals *principals,
                                const char *bytes, uintN length,
                                const char *filename, uintN lineno,
                                jsval *rval);
 
 extern JS_PUBLIC_API(JSBool)
+JS_EvaluateScriptForPrincipalsVersion(JSContext *cx, JSObject *obj,
+                                      JSPrincipals *principals,
+                                      const char *bytes, uintN length,
+                                      const char *filename, uintN lineno,
+                                      jsval *rval, JSVersion version);
+
+extern JS_PUBLIC_API(JSBool)
 JS_EvaluateUCScript(JSContext *cx, JSObject *obj,
                     const jschar *chars, uintN length,
                     const char *filename, uintN lineno,
                     jsval *rval);
 
 extern JS_PUBLIC_API(JSBool)
 JS_EvaluateUCScriptForPrincipalsVersion(JSContext *cx, JSObject *obj,
                                         JSPrincipals *principals,
diff --git a/js/src/xpconnect/loader/mozJSSubScriptLoader.cpp b/js/src/xpconnect/loader/mozJSSubScriptLoader.cpp
--- a/js/src/xpconnect/loader/mozJSSubScriptLoader.cpp
+++ b/js/src/xpconnect/loader/mozJSSubScriptLoader.cpp
@@ -55,16 +55,18 @@
 #include "nsAutoPtr.h"
 #include "nsNetUtil.h"
 #include "nsIProtocolHandler.h"
 #include "nsIFileURL.h"
 
 #include "jsapi.h"
 #include "jsdbgapi.h"
 #include "jsobj.h"
+#include "jsscript.h"
+#include "jscntxt.h"
 
 #include "mozilla/FunctionTimer.h"
 
 /* load() error msgs, XXX localize? */
 #define LOAD_ERROR_NOSERVICE "Error creating IO Service."
 #define LOAD_ERROR_NOURI "Error creating URI (invalid URL scheme?)"
 #define LOAD_ERROR_NOSCHEME "Failed to get URI scheme.  This is bad."
 #define LOAD_ERROR_URI_NOT_LOCAL "Trying to load a non-local URI."
@@ -343,18 +345,20 @@ mozJSSubScriptLoader::LoadSubScript (con
         errmsg = JS_NewStringCopyZ (cx, LOAD_ERROR_NOPRINCIPALS);
         goto return_exception;
     }
 
     /* set our own error reporter so we can report any bad things as catchable
      * exceptions, including the source/line number */
     er = JS_SetErrorReporter (cx, mozJSLoaderErrorReporter);
 
-    ok = JS_EvaluateScriptForPrincipals (cx, target_obj, jsPrincipals,
-                                         buf, len, uriStr.get(), 1, rval);        
+    ok = JS_EvaluateScriptForPrincipalsVersion(cx, target_obj, jsPrincipals,
+                                               buf, len, uriStr.get(), 1, rval,
+                                               JSVersion(script->getVersion() &
+                                                         ~js::VersionFlags::ANONFUNFIX));
     /* repent for our evil deeds */
     JS_SetErrorReporter (cx, er);
 
     cc->SetReturnValueWasSet (ok);
 
     JSPRINCIPALS_DROP(cx, jsPrincipals);
     return NS_OK;
 
diff --git a/js/src/xpconnect/tests/unit/bug596580_versioned.js b/js/src/xpconnect/tests/unit/bug596580_versioned.js
new file mode 100644
--- /dev/null
+++ b/js/src/xpconnect/tests/unit/bug596580_versioned.js
@@ -0,0 +1,4 @@
+/* Some constructs that require a high default version number. */
+let x = 12;
+function simpleGen() { yield 12; }
+var e4xy = <html><title>Huzzah!</title></html>
diff --git a/js/src/xpconnect/tests/unit/test_bug596580.js b/js/src/xpconnect/tests/unit/test_bug596580.js
new file mode 100644
--- /dev/null
+++ b/js/src/xpconnect/tests/unit/test_bug596580.js
@@ -0,0 +1,19 @@
+const Cc = Components.classes;
+const Ci = Components.interfaces;
+
+function run_test() {
+  var file = do_get_file("bug596580_versioned.js");
+  var ios = Cc["@mozilla.org/network/io-service;1"]
+              .getService(Ci.nsIIOService);
+  var uri = ios.newFileURI(file);
+  var scriptLoader = Cc["@mozilla.org/moz/jssubscript-loader;1"]
+                       .getService(Ci.mozIJSSubScriptLoader);
+  scriptLoader.loadSubScript(uri.spec);
+  version(150)
+  try {
+      scriptLoader.loadSubScript(uri.spec);
+      throw new Exception("Subscript should fail to load.");
+  } catch (e if e instanceof SyntaxError) {
+      // Okay.
+  }
+}