diff --git a/packages/babel-core/test/fixtures/plugins/nested-if-alternate/exec.js b/packages/babel-core/test/fixtures/plugins/nested-if-alternate/exec.js
new file mode 100644
index 0000000000..c9dae86ffa
--- /dev/null
+++ b/packages/babel-core/test/fixtures/plugins/nested-if-alternate/exec.js
@@ -0,0 +1,19 @@
+var res = transform('', {
+  plugins: function (b) {
+    var t = b.types;
+    return {
+      visitor: {
+        Program: function(path) {
+          if (this.done) return;
+          // if (false) { if (true) 42; } else 23;
+          var inner = t.ifStatement(t.booleanLiteral(true), t.expressionStatement(t.numericLiteral(42)), null);
+          var outer = t.ifStatement(t.booleanLiteral(false), inner, t.expressionStatement(t.numericLiteral(23)));
+          path.replaceWith(t.program([outer]));
+          this.done = true;
+        }
+      }
+    }
+  }
+});
+
+assert.equal(eval(res.code), 23);
diff --git a/packages/babel-generator/src/generators/statements.js b/packages/babel-generator/src/generators/statements.js
index 744ff256d5..4e1e62393a 100644
--- a/packages/babel-generator/src/generators/statements.js
+++ b/packages/babel-generator/src/generators/statements.js
@@ -16,8 +16,21 @@ export function IfStatement(node: Object) {
   this.push(")");
   this.space();
 
+  let needsBlock = node.alternate && t.isIfStatement(node.consequent);
+  if (needsBlock) {
+    this.push("{");
+    this.newline();
+    this.indent();
+  }
+
   this.printAndIndentOnComments(node.consequent, node);
 
+  if (needsBlock) {
+    this.dedent();
+    this.newline();
+    this.push("}");
+  }
+
   if (node.alternate) {
     if (this.isLast("}")) this.space();
     this.push("else ");
diff --git a/packages/babel-plugin-transform-react-jsx/src/index.js b/packages/babel-plugin-transform-react-jsx/src/index.js
index 2bc882b013..d19e07a8a5 100644
--- a/packages/babel-plugin-transform-react-jsx/src/index.js
+++ b/packages/babel-plugin-transform-react-jsx/src/index.js
@@ -1,5 +1,5 @@
 export default function ({ types: t }) {
-  let JSX_ANNOTATION_REGEX = /^\*\s*@jsx\s+([^\s]+)/;
+  let JSX_ANNOTATION_REGEX = /\*?\s*@jsx\s+([^\s]+)/;
 
   let visitor = require("babel-helper-builder-react-jsx")({
     pre(state) {
diff --git a/packages/babel-plugin-transform-react-jsx/test/fixtures/react/throw-if-custom-jsx-comment-sets-react-dom-multiline/actual.js b/packages/babel-plugin-transform-react-jsx/test/fixtures/react/throw-if-custom-jsx-comment-sets-react-dom-multiline/actual.js
new file mode 100644
index 0000000000..d8d5e03b67
--- /dev/null
+++ b/packages/babel-plugin-transform-react-jsx/test/fixtures/react/throw-if-custom-jsx-comment-sets-react-dom-multiline/actual.js
@@ -0,0 +1,10 @@
+/**
+ * @jsx React.DOM
+ */
+
+<Foo></Foo>;
+
+var profile = <div>
+  <img src="avatar.png" className="profile" />
+  <h3>{[user.firstName, user.lastName].join(" ")}</h3>
+</div>;
diff --git a/packages/babel-plugin-transform-react-jsx/test/fixtures/react/throw-if-custom-jsx-comment-sets-react-dom-multiline/options.json b/packages/babel-plugin-transform-react-jsx/test/fixtures/react/throw-if-custom-jsx-comment-sets-react-dom-multiline/options.json
new file mode 100644
index 0000000000..ce93ded1fe
--- /dev/null
+++ b/packages/babel-plugin-transform-react-jsx/test/fixtures/react/throw-if-custom-jsx-comment-sets-react-dom-multiline/options.json
@@ -0,0 +1,3 @@
+{
+  "throws": "The @jsx React.DOM pragma has been deprecated as of React 0.12"
+}
diff --git a/packages/babel-plugin-transform-react-jsx/test/fixtures/react/throw-if-custom-jsx-comment-sets-react-dom-simple/actual.js b/packages/babel-plugin-transform-react-jsx/test/fixtures/react/throw-if-custom-jsx-comment-sets-react-dom-simple/actual.js
new file mode 100644
index 0000000000..7454c292d6
--- /dev/null
+++ b/packages/babel-plugin-transform-react-jsx/test/fixtures/react/throw-if-custom-jsx-comment-sets-react-dom-simple/actual.js
@@ -0,0 +1,8 @@
+/* @jsx React.DOM */
+
+<Foo></Foo>;
+
+var profile = <div>
+  <img src="avatar.png" className="profile" />
+  <h3>{[user.firstName, user.lastName].join(" ")}</h3>
+</div>;
diff --git a/packages/babel-plugin-transform-react-jsx/test/fixtures/react/throw-if-custom-jsx-comment-sets-react-dom-simple/options.json b/packages/babel-plugin-transform-react-jsx/test/fixtures/react/throw-if-custom-jsx-comment-sets-react-dom-simple/options.json
new file mode 100644
index 0000000000..ce93ded1fe
--- /dev/null
+++ b/packages/babel-plugin-transform-react-jsx/test/fixtures/react/throw-if-custom-jsx-comment-sets-react-dom-simple/options.json
@@ -0,0 +1,3 @@
+{
+  "throws": "The @jsx React.DOM pragma has been deprecated as of React 0.12"
+}
diff --git a/packages/babel-plugin-transform-react-jsx/test/fixtures/react/throw-if-custom-jsx-comment-sets-react-dom-singleline/actual.js b/packages/babel-plugin-transform-react-jsx/test/fixtures/react/throw-if-custom-jsx-comment-sets-react-dom-singleline/actual.js
new file mode 100644
index 0000000000..1d050d5f12
--- /dev/null
+++ b/packages/babel-plugin-transform-react-jsx/test/fixtures/react/throw-if-custom-jsx-comment-sets-react-dom-singleline/actual.js
@@ -0,0 +1,8 @@
+// @jsx React.DOM
+
+<Foo></Foo>;
+
+var profile = <div>
+  <img src="avatar.png" className="profile" />
+  <h3>{[user.firstName, user.lastName].join(" ")}</h3>
+</div>;
diff --git a/packages/babel-plugin-transform-react-jsx/test/fixtures/react/throw-if-custom-jsx-comment-sets-react-dom-singleline/options.json b/packages/babel-plugin-transform-react-jsx/test/fixtures/react/throw-if-custom-jsx-comment-sets-react-dom-singleline/options.json
new file mode 100644
index 0000000000..ce93ded1fe
--- /dev/null
+++ b/packages/babel-plugin-transform-react-jsx/test/fixtures/react/throw-if-custom-jsx-comment-sets-react-dom-singleline/options.json
@@ -0,0 +1,3 @@
+{
+  "throws": "The @jsx React.DOM pragma has been deprecated as of React 0.12"
+}
diff --git a/packages/babel-plugin-transform-react-jsx/test/fixtures/react/throw-if-custom-jsx-comment-sets-react-dom/actual.js b/packages/babel-plugin-transform-react-jsx/test/fixtures/react/throw-if-custom-jsx-comment-sets-react-dom/actual.js
new file mode 100644
index 0000000000..ca21da88e2
--- /dev/null
+++ b/packages/babel-plugin-transform-react-jsx/test/fixtures/react/throw-if-custom-jsx-comment-sets-react-dom/actual.js
@@ -0,0 +1,8 @@
+/** @jsx React.DOM */
+
+<Foo></Foo>;
+
+var profile = <div>
+  <img src="avatar.png" className="profile" />
+  <h3>{[user.firstName, user.lastName].join(" ")}</h3>
+</div>;
diff --git a/packages/babel-plugin-transform-react-jsx/test/fixtures/react/throw-if-custom-jsx-comment-sets-react-dom/options.json b/packages/babel-plugin-transform-react-jsx/test/fixtures/react/throw-if-custom-jsx-comment-sets-react-dom/options.json
new file mode 100644
index 0000000000..ce93ded1fe
--- /dev/null
+++ b/packages/babel-plugin-transform-react-jsx/test/fixtures/react/throw-if-custom-jsx-comment-sets-react-dom/options.json
@@ -0,0 +1,3 @@
+{
+  "throws": "The @jsx React.DOM pragma has been deprecated as of React 0.12"
+}