diff --git a/core/field.js b/core/field.js
index b87a0129c..433586728 100644
--- a/core/field.js
+++ b/core/field.js
@@ -58,7 +58,11 @@ Blockly.Field = function(value, opt_validator, opt_config) {
   this.size_ = new Blockly.utils.Size(0, 0);
 
   if (opt_config) {
-    var tooltip = Blockly.utils.replaceMessageReferences(opt_config['tooltip']);
+    var tooltip = opt_config['tooltip'];
+    if (typeof tooltip == 'string') {
+      tooltip = Blockly.utils.replaceMessageReferences(
+          opt_config['tooltip']);
+    }
     tooltip && this.setTooltip(tooltip);
 
     // TODO: Possibly eventually add configurations like cursor and css class.
diff --git a/tests/mocha/field_test.js b/tests/mocha/field_test.js
index 2a2c8c545..3ae3024fb 100644
--- a/tests/mocha/field_test.js
+++ b/tests/mocha/field_test.js
@@ -359,6 +359,15 @@ suite('Abstract Fields', function() {
         });
         chai.assert.equal(field.tooltip_, 'test tooltip');
       });
+      test('JS Constructor - Dynamic', function() {
+        var returnTooltip = function() {
+          return 'dynamic tooltip text';
+        };
+        var field = new Blockly.Field('value', null, {
+          tooltip: returnTooltip
+        });
+        chai.assert.equal(field.tooltip_, returnTooltip);
+      });
       test('JSON Definition', function() {
         var field = CustomField.fromJson({
           tooltip: "test tooltip"