new file mode 100644
--- /dev/null
+++ b/js/src/jit-test/tests/basic/bug641491.js
@@ -0,0 +1,19 @@
+function f1() {
+}
+function f2() {
+}
+function f3(o) {
+    f2 = XML.prototype;
+}
+var key = Object.getOwnPropertyNames(f1)[30];
+if(key) {
+    f3 = f1[key];
+}
+gc(); 
+gc();
+try {
+for(var i=0; i<10; i++) {
+    delete f2[1];
+    f3(function() {});
+}
+} catch (e) {}

--- a/js/src/jscompartment.cpp
+++ b/js/src/jscompartment.cpp
@@ -518,43 +518,16 @@ JSCompartment::sweep(JSContext *cx, uint
      */
     for (JSCList *cursor = scripts.next; cursor != &scripts; cursor = cursor->next) {
         JSScript *script = reinterpret_cast<JSScript *>(cursor);
         if (script->hasJITCode())
             mjit::ic::PurgePICs(cx, script);
     }
 # endif
 
-    if (!types.inferenceDepth && types.inferenceEnabled) {
-        for (JSCList *cursor = scripts.next; cursor != &scripts; cursor = cursor->next) {
-            JSScript *script = reinterpret_cast<JSScript *>(cursor);
-            script->condenseTypes(cx);
-        }
-
-        types.condense(cx);
-    }
-
-    types.sweep(cx);
-
-    for (JSCList *cursor = scripts.next; cursor != &scripts; cursor = cursor->next) {
-        JSScript *script = reinterpret_cast<JSScript *>(cursor);
-        script->sweepTypes(cx);
-    }
-
-    if (!types.inferenceDepth) {
-        /* Reset the inference pool, releasing all intermediate type data. */
-        JS_FinishArenaPool(&types.pool);
-
-        /*
-         * Destroy eval'ed scripts, now that any type inference information referring
-         * to eval scripts has been removed.
-         */
-        js_DestroyScriptsToGC(cx, this);
-    }
-
 #if defined JS_METHODJIT && defined JS_MONOIC
 
     /*
      * The release interval is the frequency with which we should try to destroy
      * executable pools by releasing all JIT code in them, zero to never destroy pools.
      * Initialize counter so that the first pool will be destroyed, and eventually drive
      * the amount of JIT code in never-used compartments to zero. Don't discard anything
      * for compartments which currently have active stack frames.
@@ -578,16 +551,43 @@ JSCompartment::sweep(JSContext *cx, uint
                     mjit::ReleaseScriptCode(cx, script);
                 }
             }
         }
     }
 
 #endif
 
+    if (!types.inferenceDepth && types.inferenceEnabled) {
+        for (JSCList *cursor = scripts.next; cursor != &scripts; cursor = cursor->next) {
+            JSScript *script = reinterpret_cast<JSScript *>(cursor);
+            script->condenseTypes(cx);
+        }
+
+        types.condense(cx);
+    }
+
+    types.sweep(cx);
+
+    for (JSCList *cursor = scripts.next; cursor != &scripts; cursor = cursor->next) {
+        JSScript *script = reinterpret_cast<JSScript *>(cursor);
+        script->sweepTypes(cx);
+    }
+
+    if (!types.inferenceDepth) {
+        /* Reset the inference pool, releasing all intermediate type data. */
+        JS_FinishArenaPool(&types.pool);
+
+        /*
+         * Destroy eval'ed scripts, now that any type inference information referring
+         * to eval scripts has been removed.
+         */
+        js_DestroyScriptsToGC(cx, this);
+    }
+
     active = false;
 }
 
 void
 JSCompartment::purge(JSContext *cx)
 {
     freeLists.purge();
     dtoaCache.purge();