diff --git a/core/procedures.js b/core/procedures.js
index eef9c9d2a..98ebf41b6 100644
--- a/core/procedures.js
+++ b/core/procedures.js
@@ -140,11 +140,11 @@ Blockly.Procedures.isNameUsed = function(name, workspace, opt_exclude) {
     if (blocks[i].getProcedureDef) {
       var procName = blocks[i].getProcedureDef();
       if (Blockly.Names.equals(procName[0], name)) {
-        return false;
+        return true;
       }
     }
   }
-  return true;
+  return false;
 };
 
 /**
diff --git a/core/variables.js b/core/variables.js
index 2cf00d5f4..ac952844e 100644
--- a/core/variables.js
+++ b/core/variables.js
@@ -248,7 +248,7 @@ Blockly.Variables.createVariable = function(workspace, opt_callback, opt_type) {
                   promptAndCheckWithAlert(text);  // Recurse
                 });
           }
-          else if (!Blockly.Procedures.isNameUsed(text, workspace)) {
+          else if (Blockly.Procedures.isNameUsed(text, workspace)) {
             Blockly.alert(Blockly.Msg.PROCEDURE_ALREADY_EXISTS.replace('%1',
                 text.toLowerCase()),
                 function() {
@@ -297,7 +297,7 @@ Blockly.Variables.renameVariable = function(workspace, variable,
                   promptAndCheckWithAlert(newName);  // Recurse
                 });
           }
-          else if (!Blockly.Procedures.isNameUsed(newName, workspace)) {
+          else if (Blockly.Procedures.isNameUsed(newName, workspace)) {
             Blockly.alert(Blockly.Msg.PROCEDURE_ALREADY_EXISTS.replace('%1',
                 newName.toLowerCase()),
                 function() {
diff --git a/tests/jsunit/index.html b/tests/jsunit/index.html
index dd62a536a..940111ecb 100644
--- a/tests/jsunit/index.html
+++ b/tests/jsunit/index.html
@@ -25,6 +25,7 @@
     <script src="workspace_undo_redo_test.js"></script>
     <script src="xml_test.js"></script>
     <script src="json_test.js"></script>
+    <script src="procedures_test.js"></script>
     <script src="variable_model_test.js"></script>
     <script src="variable_map_test.js"></script>
   </body>
diff --git a/tests/jsunit/procedures_test.js b/tests/jsunit/procedures_test.js
new file mode 100644
index 000000000..10003ec74
--- /dev/null
+++ b/tests/jsunit/procedures_test.js
@@ -0,0 +1,83 @@
+/**
+ * @license
+ * Blockly Tests
+ *
+ * Copyright 2017 Google Inc.
+ * https://developers.google.com/blockly/
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+ /**
+ * @fileoverview Tests for procedures.
+ * @author marisaleung@google.com (Marisa Leung)
+ */
+'use strict';
+
+goog.require('goog.testing');
+
+var workspace;
+
+function proceduresTest_setUpWithMockBlocks() {
+  workspace = new Blockly.Workspace();
+  Blockly.defineBlocksWithJsonArray([{
+    getProcedureDef: function() {
+    },
+    'type': 'procedure_mock_block',
+    'message0': '%1',
+    'args0': [
+      {
+        'type': 'field_variable',
+        'name': 'NAME',
+        'variable': 'item'
+      }
+    ],
+  }]);
+  Blockly.Blocks['procedure_mock_block'].getProcedureDef = function() {
+    return [this.getFieldValue('NAME'), [], false];
+  };
+}
+
+function proceduresTest_tearDownWithMockBlocks() {
+  workspace.dispose();
+  delete Blockly.Blocks.procedures_mock_block;
+}
+
+
+function test_isNameUsed_NoBlocks() {
+  workspace = new Blockly.Workspace();
+  var result = Blockly.Procedures.isNameUsed('name1', workspace);
+  assertFalse(result);
+  workspace.dispose();
+}
+
+function test_isNameUsed_False() {
+  proceduresTest_setUpWithMockBlocks();
+  var block = new Blockly.Block(workspace, 'procedure_mock_block');
+  block.setFieldValue('name2', 'NAME');
+
+  var result = Blockly.Procedures.isNameUsed('name1', workspace);
+  assertFalse(result);
+  proceduresTest_tearDownWithMockBlocks();
+}
+
+function test_isNameUsed_True() {
+  proceduresTest_setUpWithMockBlocks();
+  var block = new Blockly.Block(workspace, 'procedure_mock_block');
+  block.setFieldValue('name1', 'NAME');
+
+  var result = Blockly.Procedures.isNameUsed('name1', workspace);
+  assertTrue(result);
+  proceduresTest_tearDownWithMockBlocks();
+}
+