diff --git a/CHANGELOG.md b/CHANGELOG.md
index 950b1e150b..e9d27b5838 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+# 1.12.12
+
+ * Make scope tracker more reliable to handle all edgecases.
+
 # 1.12.11
 
  * Block scope classes.
diff --git a/lib/6to5/traverse/scope.js b/lib/6to5/traverse/scope.js
index 9039501e0c..335fe9d942 100644
--- a/lib/6to5/traverse/scope.js
+++ b/lib/6to5/traverse/scope.js
@@ -4,6 +4,8 @@ var traverse = require("./index");
 var t        = require("../types");
 var _        = require("lodash");
 
+var FOR_KEYS = ["left", "init"];
+
 function Scope(parent, block) {
   this.parent = parent;
   this.block  = block;
@@ -19,29 +21,59 @@ Scope.prototype.getIds = function () {
   var self = this;
   var ids  = block._scopeIds = {};
 
-  if (t.isBlockStatement(block)) {
-    _.each(block.body, function (node) {
-      if (t.isVariableDeclaration(node) && node.kind !== "var") {
-        self.add(node, ids);
-      }
-    });
-  } else if (t.isProgram(block) || t.isFunction(block)) {
-    traverse(block, function (node, parent) {
-      if (parent !== block && t.isVariableDeclaration(node) && node.kind !== "var") {
-        return;
-      }
+  // ForStatement - left, init
 
-      if (t.isDeclaration(node)) {
-        self.add(node, ids);
-      } else if (t.isFunction(node)) {
-        return false;
-      }
+  if (t.isFor(block)) {
+    _.each(FOR_KEYS, function (key) {
+      var node = block[key];
+      if (t.isLet(node)) self.add(node, ids);
     });
-  } else if (t.isCatchClause(block)) {
+
+    block = block.body;
+  }
+
+  // Program, BlockStatement - let variables
+
+  if (t.isBlockStatement(block) || t.isProgram(block)) {
+    _.each(block.body, function (node) {
+      // check for non-var `VariableDeclaration`s
+      if (t.isLet(node)) self.add(node, ids);
+    });
+  }
+
+  // CatchClause - param
+
+  if (t.isCatchClause(block)) {
     self.add(block.param, ids);
   }
 
+  // Program, Function - var variables
+
+  if (t.isProgram(block) || t.isFunction(block)) {
+    traverse(block, function (node) {
+      if (t.isFor(node)) {
+        _.each(FOR_KEYS, function (key) {
+          var declar = node[key];
+          if (t.isVar(declar)) self.add(declar, ids);
+        });
+      }
+
+      // this block is a function so we'll stop since none of the variables
+      // declared within are accessible
+      if (t.isFunction(node)) return false;
+
+      // we've ran into a declaration!
+      // we'll let the BlockStatement scope deal with `let` declarations
+      if (t.isDeclaration(node) && !t.isLet(node)) {
+        self.add(node, ids);
+      }
+    });
+  }
+
+  // Function - params
+
   if (t.isFunction(block)) {
+    this.add(block.rest, ids);
     _.each(block.params, function (param) {
       self.add(param, ids);
     });
@@ -51,6 +83,7 @@ Scope.prototype.getIds = function () {
 };
 
 Scope.prototype.add = function (node, ids) {
+  if (!node) return;
   _.merge(ids || this.ids, t.getIds(node, true));
 };
 
diff --git a/lib/6to5/types/alias-keys.json b/lib/6to5/types/alias-keys.json
index b2f4aef530..b8920e3cd3 100644
--- a/lib/6to5/types/alias-keys.json
+++ b/lib/6to5/types/alias-keys.json
@@ -35,9 +35,9 @@
   "ClassDeclaration": ["Statement", "Declaration", "Class"],
   "ClassExpression":  ["Class"],
 
-  "ForOfStatement": ["Statement", "For"],
-  "ForInStatement": ["Statement", "For"],
-  "ForStatement":   ["Statement", "For"],
+  "ForOfStatement": ["Statement", "For", "Scope"],
+  "ForInStatement": ["Statement", "For", "Scope"],
+  "ForStatement":   ["Statement", "For", "Scope"],
 
   "ObjectPattern": ["Pattern"],
   "ArrayPattern":  ["Pattern"],
diff --git a/lib/6to5/types/index.js b/lib/6to5/types/index.js
index c921215e4f..28d3fc17ad 100644
--- a/lib/6to5/types/index.js
+++ b/lib/6to5/types/index.js
@@ -185,6 +185,14 @@ t.getIds = function (node, map, ignoreTypes) {
   return ids;
 };
 
+t.isLet = function (node) {
+  return t.isVariableDeclaration(node) && (node.kind !== "var" || node._let);
+};
+
+t.isVar = function (node) {
+  return t.isVariableDeclaration(node, { kind: "var" }) && !node._let;
+};
+
 t.getIds.nodes = {
   AssignmentExpression: "left",
   ImportSpecifier: "id",
diff --git a/test/fixtures/transformation/let-scoping/duplicate-in-upper-scope/exec.js b/test/fixtures/transformation/let-scoping/duplicate-in-upper-scope/exec.js
new file mode 100644
index 0000000000..b0c9c0f6c1
--- /dev/null
+++ b/test/fixtures/transformation/let-scoping/duplicate-in-upper-scope/exec.js
@@ -0,0 +1,5 @@
+let x = [0];
+for (let x of x) {
+  assert.equal(x, 0);
+}
+assert.deepEqual(x, [0]);