diff --git a/include/chaiscript/language/chaiscript_optimizer.hpp b/include/chaiscript/language/chaiscript_optimizer.hpp
index e8048eb3..e6d11544 100644
--- a/include/chaiscript/language/chaiscript_optimizer.hpp
+++ b/include/chaiscript/language/chaiscript_optimizer.hpp
@@ -397,11 +397,11 @@ namespace chaiscript {
                                         assert(children.size() == 1);
                                         chaiscript::eval::detail::Scope_Push_Pop spp(t_ss);
 
-                                        int i = start_int;
-                                        t_ss.add_object(id, var(&i));
+                                        auto i = std::make_shared<int>(start_int);
+                                        t_ss.add_object(id, var(i));
 
                                         try {
-                                          for (; i < end_int; ++i) {
+                                          for (; *i < end_int; ++(*i)) {
                                             try {
                                               // Body of Loop
                                               children[0]->eval(t_ss);
diff --git a/unittests/future_assign.chai b/unittests/future_assign.chai
new file mode 100644
index 00000000..41152169
--- /dev/null
+++ b/unittests/future_assign.chai
@@ -0,0 +1,21 @@
+// Regression test for #635: Segfault when using := in async function
+// with optimized for loop. The := operator copies raw pointers from the
+// loop variable, which is stack-allocated in the optimized for loop.
+// When the function returns, the stack is unwound and pointers dangle.
+
+var func = fun(){
+  var ret = 0;
+  for (var i = 0; i < 50000; ++i) {
+    ret := i;
+  }
+  return ret;
+}
+
+var fut1 = async(func);
+var fut2 = async(func);
+
+// This triggers Boxed_Number::get_as<int> on the future results
+// which would crash if the pointers are dangling
+// := creates an alias, so ret ends up as 50000 (loop exit value of i)
+assert_equal(50000, fut1.get())
+assert_equal(50000, fut2.get())