diff --git a/resources/celerity/map.php b/resources/celerity/map.php
--- a/resources/celerity/map.php
+++ b/resources/celerity/map.php
@@ -382,7 +382,7 @@
     'rsrc/js/application/aphlict/behavior-desktop-notifications-control.js' => 'edd1ba66',
     'rsrc/js/application/auth/behavior-persona-login.js' => '9414ff18',
     'rsrc/js/application/calendar/behavior-day-view.js' => '4b3c4443',
-    'rsrc/js/application/calendar/behavior-event-all-day.js' => '937bb700',
+    'rsrc/js/application/calendar/behavior-event-all-day.js' => 'b41537c9',
     'rsrc/js/application/calendar/behavior-month-view.js' => 'fe33e256',
     'rsrc/js/application/calendar/behavior-recurring-edit.js' => '5f1c4d5f',
     'rsrc/js/application/config/behavior-reorder-fields.js' => 'b6993408',
@@ -651,7 +651,7 @@
     'javelin-behavior-editengine-reorder-configs' => 'd7a74243',
     'javelin-behavior-editengine-reorder-fields' => 'b59e1e96',
     'javelin-behavior-error-log' => '6882e80a',
-    'javelin-behavior-event-all-day' => '937bb700',
+    'javelin-behavior-event-all-day' => 'b41537c9',
     'javelin-behavior-fancy-datepicker' => '568931f3',
     'javelin-behavior-global-drag-and-drop' => '960f6a39',
     'javelin-behavior-herald-rule-editor' => '7ebaeed3',
diff --git a/src/aphront/httpparametertype/AphrontBoolHTTPParameterType.php b/src/aphront/httpparametertype/AphrontBoolHTTPParameterType.php
--- a/src/aphront/httpparametertype/AphrontBoolHTTPParameterType.php
+++ b/src/aphront/httpparametertype/AphrontBoolHTTPParameterType.php
@@ -3,8 +3,21 @@
 final class AphrontBoolHTTPParameterType
   extends AphrontHTTPParameterType {
 
+  protected function getParameterExists(AphrontRequest $request, $key) {
+    if ($request->getExists($key)) {
+      return true;
+    }
+
+    $checkbox_key = $this->getCheckboxKey($key);
+    if ($request->getExists($checkbox_key)) {
+      return true;
+    }
+
+    return false;
+  }
+
   protected function getParameterValue(AphrontRequest $request, $key) {
-    return $request->getBool($key);
+    return (bool)$request->getBool($key);
   }
 
   protected function getParameterTypeName() {
@@ -26,4 +39,8 @@
     );
   }
 
+  public function getCheckboxKey($key) {
+    return "{$key}.exists";
+  }
+
 }
diff --git a/src/applications/calendar/editor/PhabricatorCalendarEventEditEngine.php b/src/applications/calendar/editor/PhabricatorCalendarEventEditEngine.php
--- a/src/applications/calendar/editor/PhabricatorCalendarEventEditEngine.php
+++ b/src/applications/calendar/editor/PhabricatorCalendarEventEditEngine.php
@@ -90,8 +90,8 @@
         ->setValue($object->getName()),
       id(new PhabricatorBoolEditField())
         ->setKey('isAllDay')
-        ->setLabel(pht('All Day'))
         ->setOptions(pht('Normal Event'), pht('All Day Event'))
+        ->setAsCheckbox(true)
         ->setTransactionType(
           PhabricatorCalendarEventAllDayTransaction::TRANSACTIONTYPE)
         ->setDescription(pht('Marks this as an all day event.'))
diff --git a/src/applications/calendar/xaction/PhabricatorCalendarEventAllDayTransaction.php b/src/applications/calendar/xaction/PhabricatorCalendarEventAllDayTransaction.php
--- a/src/applications/calendar/xaction/PhabricatorCalendarEventAllDayTransaction.php
+++ b/src/applications/calendar/xaction/PhabricatorCalendarEventAllDayTransaction.php
@@ -39,7 +39,7 @@
   public function getTitle() {
     if ($this->getNewValue()) {
       return pht(
-        '%s changed this as an all day event.',
+        '%s changed this to an all day event.',
         $this->renderAuthor());
     } else {
       return pht(
diff --git a/src/applications/transactions/editfield/PhabricatorBoolEditField.php b/src/applications/transactions/editfield/PhabricatorBoolEditField.php
--- a/src/applications/transactions/editfield/PhabricatorBoolEditField.php
+++ b/src/applications/transactions/editfield/PhabricatorBoolEditField.php
@@ -4,6 +4,7 @@
   extends PhabricatorEditField {
 
   private $options;
+  private $asCheckbox;
 
   public function setOptions($off_label, $on_label) {
     $this->options = array(
@@ -17,6 +18,15 @@
     return $this->options;
   }
 
+  public function setAsCheckbox($as_checkbox) {
+    $this->asCheckbox = $as_checkbox;
+    return $this;
+  }
+
+  public function getAsCheckbox() {
+    return $this->asCheckbox;
+  }
+
   protected function newControl() {
     $options = $this->getOptions();
 
@@ -27,8 +37,22 @@
       );
     }
 
-    return id(new AphrontFormSelectControl())
-      ->setOptions($options);
+    if ($this->getAsCheckbox()) {
+      $key = $this->getKey();
+      $value = $this->getValueForControl();
+      $checkbox_key = $this->newHTTPParameterType()
+        ->getCheckboxKey($key);
+      $id = $this->getControlID();
+
+      $control = id(new AphrontFormCheckboxControl())
+        ->setCheckboxKey($checkbox_key)
+        ->addCheckbox($key, '1', $options['1'], $value, $id);
+    } else {
+      $control = id(new AphrontFormSelectControl())
+        ->setOptions($options);
+    }
+
+    return $control;
   }
 
   protected function newHTTPParameterType() {
diff --git a/src/applications/transactions/storage/PhabricatorApplicationTransaction.php b/src/applications/transactions/storage/PhabricatorApplicationTransaction.php
--- a/src/applications/transactions/storage/PhabricatorApplicationTransaction.php
+++ b/src/applications/transactions/storage/PhabricatorApplicationTransaction.php
@@ -553,8 +553,16 @@
             return true;
           }
 
-          if (!is_array($old) && !strlen($old)) {
-            return true;
+          if (!is_array($old)) {
+            if (!strlen($old)) {
+              return true;
+            }
+
+            // The integer 0 is also uninteresting by default; this is often
+            // an "off" flag for something like "All Day Event".
+            if ($old === 0) {
+              return true;
+            }
           }
 
           break;
diff --git a/src/view/form/control/AphrontFormCheckboxControl.php b/src/view/form/control/AphrontFormCheckboxControl.php
--- a/src/view/form/control/AphrontFormCheckboxControl.php
+++ b/src/view/form/control/AphrontFormCheckboxControl.php
@@ -3,6 +3,16 @@
 final class AphrontFormCheckboxControl extends AphrontFormControl {
 
   private $boxes = array();
+  private $checkboxKey;
+
+  public function setCheckboxKey($checkbox_key) {
+    $this->checkboxKey = $checkbox_key;
+    return $this;
+  }
+
+  public function getCheckboxKey() {
+    return $this->checkboxKey;
+  }
 
   public function addCheckbox(
     $name,
@@ -52,6 +62,23 @@
         phutil_tag('th', array(), $label),
       ));
     }
+
+    // When a user submits a form with a checkbox unchecked, the browser
+    // doesn't submit anything to the server. This hidden key lets the server
+    // know that the checkboxes were present on the client, the user just did
+    // not select any of them.
+
+    $checkbox_key = $this->getCheckboxKey();
+    if ($checkbox_key) {
+      $rows[] = phutil_tag(
+        'input',
+        array(
+          'type' => 'hidden',
+          'name' => $checkbox_key,
+          'value' => 1,
+        ));
+    }
+
     return phutil_tag(
       'table',
       array('class' => 'aphront-form-control-checkbox-layout'),
diff --git a/webroot/rsrc/js/application/calendar/behavior-event-all-day.js b/webroot/rsrc/js/application/calendar/behavior-event-all-day.js
--- a/webroot/rsrc/js/application/calendar/behavior-event-all-day.js
+++ b/webroot/rsrc/js/application/calendar/behavior-event-all-day.js
@@ -6,7 +6,7 @@
   var all_day = JX.$(config.allDayID);
 
   JX.DOM.listen(all_day, 'change', null, function() {
-    var is_all_day = !!parseInt(all_day.value, 10);
+    var is_all_day = !!all_day.checked;
 
     for (var ii = 0; ii < config.controlIDs.length; ii++) {
       var control = JX.$(config.controlIDs[ii]);