diff --git a/core/field.js b/core/field.js
index 9b1beb8bb..6b0968e94 100644
--- a/core/field.js
+++ b/core/field.js
@@ -621,6 +621,12 @@ Blockly.Field.prototype.setValue = function(newValue) {
     // No change if null.
     return;
   }
+  // Validate input.
+  var validated = this.callValidator(newValue);
+  if (validated !== null) {
+    newValue = validated;
+  }
+  // Check for change.
   var oldValue = this.getValue();
   if (oldValue == newValue) {
     return;
diff --git a/core/field_number.js b/core/field_number.js
index fd144f04d..10e0efdf0 100644
--- a/core/field_number.js
+++ b/core/field_number.js
@@ -45,10 +45,10 @@ goog.require('Blockly.FieldTextInput');
  */
 Blockly.FieldNumber = function(opt_value, opt_min, opt_max, opt_precision,
     opt_validator) {
+  this.setConstraints(opt_min, opt_max, opt_precision);
   opt_value = (opt_value && !isNaN(opt_value)) ? String(opt_value) : '0';
   Blockly.FieldNumber.superClass_.constructor.call(
       this, opt_value, opt_validator);
-  this.setConstraints(opt_min, opt_max, opt_precision);
 };
 goog.inherits(Blockly.FieldNumber, Blockly.FieldTextInput);
 
@@ -95,7 +95,6 @@ Blockly.FieldNumber.prototype.setConstraints = function(min, max, precision) {
   this.min_ = isNaN(min) ? -Infinity : min;
   max = parseFloat(max);
   this.max_ = isNaN(max) ? Infinity : max;
-  this.setValue(this.callValidator(this.getValue()));
 };
 
 /**