diff --git a/core/block.js b/core/block.js
index 1bbd06dbe..6c36c989b 100644
--- a/core/block.js
+++ b/core/block.js
@@ -12,6 +12,7 @@
 
 goog.provide('Blockly.Block');
 
+goog.require('Blockly.ASTNode');
 goog.require('Blockly.Blocks');
 goog.require('Blockly.Connection');
 goog.require('Blockly.Events');
@@ -1306,23 +1307,94 @@ Blockly.Block.prototype.setCollapsed = function(collapsed) {
 Blockly.Block.prototype.toString = function(opt_maxLength, opt_emptyToken) {
   var text = [];
   var emptyFieldPlaceholder = opt_emptyToken || '?';
-  for (var i = 0, input; (input = this.inputList[i]); i++) {
-    if (input.name == Blockly.Block.COLLAPSED_INPUT_NAME) {
-      continue;
+
+  // Temporarily set flag to navigate to all fields.
+  var prevNavigateFields = Blockly.ASTNode.NAVIGATE_ALL_FIELDS;
+  Blockly.ASTNode.NAVIGATE_ALL_FIELDS = true;
+
+  var node = Blockly.ASTNode.createBlockNode(this);
+  var rootNode = node;
+
+  /**
+   * Whether or not to add parentheses around an input.
+   * @param {!Blockly.Connection} connection The connection.
+   * @return {boolean} True if we should add parentheses around the input.
+   */
+  function shouldAddParentheses(connection) {
+    var checks = connection.getCheck();
+    if (!checks && connection.targetConnection) {
+      checks = connection.targetConnection.getCheck();
     }
-    for (var j = 0, field; (field = input.fieldRow[j]); j++) {
-      text.push(field.getText());
+    return !!checks && (checks.indexOf('Boolean') != -1 ||
+        checks.indexOf('Number') != -1);
+  }
+
+  /**
+   * Check that we haven't circled back to the original root node.
+   */
+  function checkRoot() {
+    if (node && node.getType() == rootNode.getType() &&
+        node.getLocation() == rootNode.getLocation()) {
+      node = null;
     }
-    if (input.connection) {
-      var child = input.connection.targetBlock();
-      if (child) {
-        text.push(child.toString(undefined, opt_emptyToken));
-      } else {
-        text.push(emptyFieldPlaceholder);
+  }
+
+  // Traverse the AST building up our text string.
+  while (node) {
+    switch (node.getType()) {
+      case Blockly.ASTNode.types.INPUT:
+        var connection = /** @type {!Blockly.Connection} */ (node.getLocation());
+        if (!node.in()) {
+          text.push(emptyFieldPlaceholder);
+        } else if (shouldAddParentheses(connection)) {
+          text.push('(');
+        }
+        break;
+      case Blockly.ASTNode.types.FIELD:
+        var field = /** @type {Blockly.Field} */ (node.getLocation());
+        if (field.name != Blockly.Block.COLLAPSED_FIELD_NAME) {
+          text.push(field.getText());
+        }
+        break;
+    }
+
+    var current = node;
+    node = current.in() || current.next();
+    if (!node) {
+      // Can't go in or next, keep going out until we can go next.
+      node = current.out();
+      checkRoot();
+      while (node && !node.next()) {
+        node = node.out();
+        checkRoot();
+        // If we hit an input on the way up, possibly close out parentheses.
+        if (node && node.getType() == Blockly.ASTNode.types.INPUT &&
+            shouldAddParentheses(
+                /** @type {!Blockly.Connection} */ (node.getLocation()))) {
+          text.push(')');
+        }
+      }
+      if (node) {
+        node = node.next();
       }
     }
   }
-  text = text.join(' ').trim() || '???';
+
+  // Restore state of NAVIGATE_ALL_FIELDS.
+  Blockly.ASTNode.NAVIGATE_ALL_FIELDS = prevNavigateFields;
+
+  // Run through our text array and simplify expression to remove parentheses
+  // around single field blocks.
+  for (var i = 2, l = text.length; i < l; i++) {
+    if (text[i - 2] == '(' && text[i] == ')') {
+      text[i - 2] = text[i - 1];
+      text.splice(i - 1, 2);
+      l -= 2;
+    }
+  }
+
+  // Join the text array, removing spaces around added paranthesis.
+  text = text.join(' ').replace(/(\() | (\))/gmi, '$1$2').trim() || '???';
   if (opt_maxLength) {
     // TODO: Improve truncation so that text from this block is given priority.
     // E.g. "1+2+3+4+5+6+7+8+9=0" should be "...6+7+8+9=0", not "1+2+3+4+5...".
diff --git a/tests/mocha/block_test.js b/tests/mocha/block_test.js
index 58e20aa69..08f11a84b 100644
--- a/tests/mocha/block_test.js
+++ b/tests/mocha/block_test.js
@@ -1680,4 +1680,116 @@ suite('Blocks', function() {
       });
     });
   });
+  suite('toString', function() {
+    var toStringTests = [
+      {
+        name: 'statement block',
+        xml: '<block type="controls_repeat_ext">' +
+          '<value name="TIMES">' +
+            '<shadow type="math_number">' +
+              '<field name="NUM">10</field>' +
+          '</shadow>' +
+          '</value>' +
+        '</block>',
+        toString: 'repeat 10 times do ?',
+      },
+      {
+        name: 'nested statement blocks',
+        xml: '<block type="controls_repeat_ext">' +
+          '<value name="TIMES">' +
+            '<shadow type="math_number">' +
+              '<field name="NUM">10</field>' +
+            '</shadow>' +
+          '</value>' +
+          '<statement name="DO">' +
+            '<block type="controls_if"></block>' +
+          '</statement>' +
+        '</block>',
+        toString: 'repeat 10 times do if ? do ?',
+      },
+      {
+        name: 'nested Boolean output blocks',
+        xml: '<block type="controls_if">' +
+          '<value name="IF0">' +
+            '<block type="logic_compare">' +
+              '<field name="OP">EQ</field>' +
+              '<value name="A">' +
+                '<block type="logic_operation">' +
+                  '<field name="OP">AND</field>' +
+                '</block>' +
+              '</value>' +
+            '</block>' +
+          '</value>' +
+        '</block>',
+        toString: 'if ((? and ?) = ?) do ?',
+      },
+      {
+        name: 'output block',
+        xml: '<block type="math_single">' +
+          '<field name="OP">ROOT</field>' +
+          '<value name="NUM">' +
+            '<shadow type="math_number">' +
+              '<field name="NUM">9</field>' +
+            '</shadow>' +
+          '</value>' +
+        '</block>',
+        toString: 'square root 9',
+      },
+      {
+        name: 'nested Number output blocks',
+        xml: '<block type="math_arithmetic">' +
+          '<field name="OP">ADD</field>' +
+          '<value name="A">' +
+            '<shadow type="math_number">' +
+              '<field name="NUM">1</field>' +
+            '</shadow>' +
+            '<block type="math_arithmetic">' +
+              '<field name="OP">MULTIPLY</field>' +
+              '<value name="A">' +
+                '<shadow type="math_number">' +
+                  '<field name="NUM">10</field>' +
+                '</shadow>' +
+              '</value>' +
+              '<value name="B">' +
+                '<shadow type="math_number">' +
+                  '<field name="NUM">5</field>' +
+                '</shadow>' +
+              '</value>' +
+            '</block>' +
+          '</value>' +
+          '<value name="B">' +
+            '<shadow type="math_number">' +
+              '<field name="NUM">3</field>' +
+            '</shadow>' +
+          '</value>' +
+        '</block>',
+        toString: '(10 × 5) + 3',
+      },
+      {
+        name: 'nested String output blocks',
+        xml: '<block type="text_join">' +
+          '<mutation items="2"></mutation>' +
+          '<value name="ADD0">' +
+            '<block type="text">' +
+              '<field name="TEXT">Hello</field>' +
+            '</block>' +
+          '</value>' +
+          '<value name="ADD1">' +
+            '<block type="text">' +
+              '<field name="TEXT">World</field>' +
+            '</block>' +
+          '</value>' +
+        '</block>',
+        toString: 'create text with “ Hello ” “ World ”',
+      },
+    ];
+    // Create mocha test cases for each toString test.
+    toStringTests.forEach(function(t) {
+      test(t.name, function() {
+        var block = Blockly.Xml.domToBlock(Blockly.Xml.textToDom(t.xml),
+            this.workspace);
+        chai.assert.equal(block.toString(), t.toString);
+      });
+    });
+  });
 });
diff --git a/tests/mocha/index.html b/tests/mocha/index.html
index 078dc71d7..3e238977d 100644
--- a/tests/mocha/index.html
+++ b/tests/mocha/index.html
@@ -12,6 +12,7 @@
     <script src="../../generators/php.js"></script>
     <script src="../../generators/python.js"></script>
     <script src="../../msg/messages.js"></script>
+    <script src="../../blocks/loops.js"></script>
     <script src="../../blocks/lists.js"></script>
     <script src="../../blocks/logic.js"></script>
     <script src="../../blocks/math.js"></script>
diff --git a/tests/mocha/workspace_test.js b/tests/mocha/workspace_test.js
index 9693922ae..db6a2e280 100644
--- a/tests/mocha/workspace_test.js
+++ b/tests/mocha/workspace_test.js
@@ -669,15 +669,15 @@ function testAWorkspace() {
 
     test('After dispose', function() {
       this.blockA.dispose();
-      chai.assert.isNull(this.workspace.getBlockById(this.blockA));
+      chai.assert.isNull(this.workspace.getBlockById(this.blockA.id));
       chai.assert.equal(
           this.workspace.getBlockById(this.blockB.id), this.blockB);
     });
 
     test('After clear', function() {
       this.workspace.clear();
-      chai.assert.isNull(this.workspace.getBlockById(this.blockA));
-      chai.assert.isNull(this.workspace.getBlockById(this.blockB));
+      chai.assert.isNull(this.workspace.getBlockById(this.blockA.id));
+      chai.assert.isNull(this.workspace.getBlockById(this.blockB.id));
     });
   });