diff --git a/packages/babel-types/package.json b/packages/babel-types/package.json
index 73f343ab0785..0d4caf54310c 100644
--- a/packages/babel-types/package.json
+++ b/packages/babel-types/package.json
@@ -13,6 +13,7 @@
     "to-fast-properties": "^1.0.1"
   },
   "devDependencies": {
+    "babel-generator": "7.0.0-alpha.9",
     "babylon": "^7.0.0-beta.8"
   }
 }
diff --git a/packages/babel-types/src/converters.js b/packages/babel-types/src/converters.js
index b6510c88d5f8..a76d6bd776b8 100644
--- a/packages/babel-types/src/converters.js
+++ b/packages/babel-types/src/converters.js
@@ -10,6 +10,71 @@ export function toComputedKey(node: Object, key: Object = node.key || node.prope
   return key;
 }
 
+
+function gatherSequenceExpressions(nodes: Array<Object>, scope: Scope, declars: Array<Object>): ?Object {
+  const exprs = [];
+  let ensureLastUndefined = true;
+
+  for (const node of nodes) {
+    ensureLastUndefined = false;
+
+    if (t.isExpression(node)) {
+      exprs.push(node);
+    } else if (t.isExpressionStatement(node)) {
+      exprs.push(node.expression);
+    } else if (t.isVariableDeclaration(node)) {
+      if (node.kind !== "var") return; // bailed
+
+      for (const declar of (node.declarations: Array)) {
+        const bindings = t.getBindingIdentifiers(declar);
+        for (const key in bindings) {
+          declars.push({
+            kind: node.kind,
+            id: bindings[key],
+          });
+        }
+
+        if (declar.init) {
+          exprs.push(t.assignmentExpression("=", declar.id, declar.init));
+        }
+      }
+
+      ensureLastUndefined = true;
+    } else if (t.isIfStatement(node)) {
+      const consequent = node.consequent ?
+        gatherSequenceExpressions([node.consequent], scope, declars) :
+        scope.buildUndefinedNode();
+      const alternate = node.alternate ?
+        gatherSequenceExpressions([node.alternate], scope, declars) :
+        scope.buildUndefinedNode();
+      if (!consequent || !alternate) return; // bailed
+
+      exprs.push(t.conditionalExpression(node.test, consequent, alternate));
+    } else if (t.isBlockStatement(node)) {
+      const body = gatherSequenceExpressions(node.body, scope, declars);
+      if (!body) return; // bailed
+
+      exprs.push(body);
+    } else if (t.isEmptyStatement(node)) {
+      // empty statement so ensure the last item is undefined if we're last
+      ensureLastUndefined = true;
+    } else {
+      // bailed, we can't turn this statement into an expression
+      return;
+    }
+  }
+
+  if (ensureLastUndefined) {
+    exprs.push(scope.buildUndefinedNode());
+  }
+
+  if (exprs.length === 1) {
+    return exprs[0];
+  } else {
+    return t.sequenceExpression(exprs);
+  }
+}
+
 /**
  * Turn an array of statement `nodes` into a `SequenceExpression`.
  *
@@ -23,80 +88,14 @@ export function toSequenceExpression(nodes: Array<Object>, scope: Scope): ?Objec
   if (!nodes || !nodes.length) return;
 
   const declars = [];
-  let bailed = false;
-
-  const result = convert(nodes);
-  if (bailed) return;
+  const result = gatherSequenceExpressions(nodes, scope, declars);
+  if (!result) return;
 
-  for (let i = 0; i < declars.length; i++) {
-    scope.push(declars[i]);
+  for (const declar of declars) {
+    scope.push(declar);
   }
 
   return result;
-
-  function convert(nodes) {
-    let ensureLastUndefined = false;
-    const exprs = [];
-
-    for (const node of (nodes: Array)) {
-      if (t.isExpression(node)) {
-        exprs.push(node);
-      } else if (t.isExpressionStatement(node)) {
-        exprs.push(node.expression);
-      } else if (t.isVariableDeclaration(node)) {
-        if (node.kind !== "var") return bailed = true; // bailed
-
-        for (const declar of (node.declarations: Array)) {
-          const bindings = t.getBindingIdentifiers(declar);
-          for (const key in bindings) {
-            declars.push({
-              kind: node.kind,
-              id: bindings[key],
-            });
-          }
-
-          if (declar.init) {
-            exprs.push(t.assignmentExpression("=", declar.id, declar.init));
-          }
-        }
-
-        ensureLastUndefined = true;
-        continue;
-      } else if (t.isIfStatement(node)) {
-        const consequent = node.consequent ? convert([node.consequent]) : scope.buildUndefinedNode();
-        const alternate = node.alternate ? convert([node.alternate]) : scope.buildUndefinedNode();
-
-        if (consequent === true || alternate === true) {
-          return bailed = true;
-        }
-
-        exprs.push(t.conditionalExpression(node.test, consequent, alternate));
-      } else if (t.isBlockStatement(node)) {
-        exprs.push(convert(node.body));
-      } else if (t.isEmptyStatement(node)) {
-        // empty statement so ensure the last item is undefined if we're last
-        ensureLastUndefined = true;
-        continue;
-      } else {
-        // bailed, we can't turn this statement into an expression
-        return bailed = true;
-      }
-
-      ensureLastUndefined = false;
-    }
-
-    if (ensureLastUndefined || exprs.length === 0) {
-      exprs.push(scope.buildUndefinedNode());
-    }
-
-    //
-
-    if (exprs.length === 1) {
-      return exprs[0];
-    } else {
-      return t.sequenceExpression(exprs);
-    }
-  }
 }
 
 export function toKeyAlias(node: Object, key: Object = node.key): string {
diff --git a/packages/babel-types/test/converters.js b/packages/babel-types/test/converters.js
index 43e1e887a7e2..31584eb6e40b 100644
--- a/packages/babel-types/test/converters.js
+++ b/packages/babel-types/test/converters.js
@@ -1,5 +1,16 @@
 import * as t from "../lib";
 import { assert } from "chai";
+import { parse } from "babylon";
+import generate from "babel-generator";
+
+function parseCode(string) {
+  return parse(string, {
+    allowReturnOutsideFunction: true,
+  }).program.body[0];
+}
+function generateCode(node) {
+  return generate(node).code;
+}
 
 describe("converters", function () {
   it("toIdentifier", function () {
@@ -149,4 +160,105 @@ describe("converters", function () {
       t.assertProgram(node);
     });
   });
+  describe("toSequenceExpression", function () {
+    let scope;
+    const undefinedNode = t.identifier("undefined");
+    beforeEach(function () {
+      scope = [];
+      scope.buildUndefinedNode = function () {
+        return undefinedNode;
+      };
+    });
+    it("gathers nodes into sequence", function () {
+      const node = t.identifier("a");
+      const sequence = t.toSequenceExpression([undefinedNode, node], scope);
+      t.assertSequenceExpression(sequence);
+      assert.equal(sequence.expressions[0], undefinedNode);
+      assert.equal(sequence.expressions[1], node);
+      t.assertIdentifier(node);
+    });
+    it("avoids sequence for single node", function () {
+      const node = t.identifier("a");
+      let sequence = t.toSequenceExpression([node], scope);
+      assert.equal(sequence, node);
+
+      const block = t.blockStatement([t.expressionStatement(node)]);
+      sequence = t.toSequenceExpression([block], scope);
+      assert.equal(sequence, node);
+    });
+    it("gathers expression", function () {
+      const node = t.identifier("a");
+      const sequence = t.toSequenceExpression([undefinedNode, node], scope);
+      assert.equal(sequence.expressions[1], node);
+    });
+    it("gathers expression statement", function () {
+      const node = t.expressionStatement(t.identifier("a"));
+      const sequence = t.toSequenceExpression([undefinedNode, node], scope);
+      assert.equal(sequence.expressions[1], node.expression);
+    });
+    it("gathers var declarations", function () {
+      const node = parseCode("var a, b = 1;");
+      const sequence = t.toSequenceExpression([undefinedNode, node], scope);
+      t.assertIdentifier(scope[0].id, { name: "a" });
+      t.assertIdentifier(scope[1].id, { name: "b" });
+      assert.equal(generateCode(sequence.expressions[1]), "b = 1");
+      assert.equal(generateCode(sequence.expressions[2]), "undefined");
+    });
+    it("skips undefined if expression after var declaration", function () {
+      const node = parseCode("{ var a, b = 1; true }");
+      const sequence = t.toSequenceExpression([undefinedNode, node], scope);
+      assert.equal(generateCode(sequence.expressions[1]), "b = 1, true");
+    });
+    it("bails on let and const declarations", function () {
+      let node = parseCode("let a, b = 1;");
+      let sequence = t.toSequenceExpression([undefinedNode, node], scope);
+      assert.isUndefined(sequence);
+
+      node = parseCode("const b = 1;");
+      sequence = t.toSequenceExpression([undefinedNode, node], scope);
+      assert.isUndefined(sequence);
+    });
+    it("gathers if statements", function () {
+      let node = parseCode("if (true) { true }");
+      let sequence = t.toSequenceExpression([undefinedNode, node], scope);
+      assert.equal(generateCode(sequence.expressions[1]), "true ? true : undefined");
+
+      node = parseCode("if (true) { true } else { b }");
+      sequence = t.toSequenceExpression([undefinedNode, node], scope);
+      assert.equal(generateCode(sequence.expressions[1]), "true ? true : b");
+    });
+    it("bails in if statements if recurse bails", function () {
+      let node = parseCode("if (true) { return }");
+      let sequence = t.toSequenceExpression([undefinedNode, node], scope);
+      assert.isUndefined(sequence);
+
+      node = parseCode("if (true) { true } else { return }");
+      sequence = t.toSequenceExpression([undefinedNode, node], scope);
+      assert.isUndefined(sequence);
+    });
+    it("gathers block statements", function () {
+      let node = parseCode("{ a }");
+      let sequence = t.toSequenceExpression([undefinedNode, node], scope);
+      assert.equal(generateCode(sequence.expressions[1]), "a");
+
+      node = parseCode("{ a; b; }");
+      sequence = t.toSequenceExpression([undefinedNode, node], scope);
+      assert.equal(generateCode(sequence.expressions[1]), "a, b");
+    });
+    it("bails in block statements if recurse bails", function () {
+      const node = parseCode("{ return }");
+      const sequence = t.toSequenceExpression([undefinedNode, node], scope);
+      assert.isUndefined(sequence);
+    });
+    it("gathers empty statements", function () {
+      const node = parseCode(";");
+      const sequence = t.toSequenceExpression([undefinedNode, node], scope);
+      assert.equal(generateCode(sequence.expressions[1]), "undefined");
+    });
+    it("skips empty statement if expression afterwards", function () {
+      const node = parseCode("{ ; true }");
+      const sequence = t.toSequenceExpression([undefinedNode, node], scope);
+      assert.equal(generateCode(sequence.expressions[1]), "true");
+    });
+  });
 });