diff --git a/core/misc/dialog/dialog.position.js b/core/misc/dialog/dialog.position.js
index 7678646..e90bef7 100644
--- a/core/misc/dialog/dialog.position.js
+++ b/core/misc/dialog/dialog.position.js
@@ -19,47 +19,69 @@
   /**
    * Resets the current options for positioning.
    *
-   * This is used as a window resize and scroll callback to reposition the
-   * jQuery UI dialog. Although not a built-in jQuery UI option, this can
-   * be disabled by setting autoResize: false in the options array when creating
-   * a new {@link Drupal.dialog}.
-   *
-   * @function Drupal.dialog~resetSize
-   *
-   * @param {jQuery.Event} event
-   *   The event triggered.
-   *
-   * @fires event:dialogContentResize
+   * @param {boolean} isModal
+   *   Whether the dialog is a modal.
    */
-  function resetSize(event) {
-    var positionOptions = ['width', 'height', 'minWidth', 'minHeight', 'maxHeight', 'maxWidth', 'position'];
-    var adjustedOptions = {};
-    var windowHeight = $(window).height();
-    var option;
-    var optionValue;
-    var adjustedValue;
-    for (var n = 0; n < positionOptions.length; n++) {
-      option = positionOptions[n];
-      optionValue = event.data.settings[option];
-      if (optionValue) {
-        // jQuery UI does not support percentages on heights, convert to pixels.
-        if (typeof optionValue === 'string' && /%$/.test(optionValue) && /height/i.test(option)) {
-          // Take offsets in account.
-          windowHeight -= displace.offsets.top + displace.offsets.bottom;
-          adjustedValue = parseInt(0.01 * parseInt(optionValue, 10) * windowHeight, 10);
-          // Don't force the dialog to be bigger vertically than needed.
-          if (option === 'height' && event.data.$element.parent().outerHeight() < adjustedValue) {
-            adjustedValue = 'auto';
+  function resetSize(isModal) {
+    /**
+     * Resets the current options for positioning.
+     *
+     * This is used as a window resize and scroll callback to reposition the
+     * jQuery UI dialog. Although not a built-in jQuery UI option, this can
+     * be disabled by setting autoResize: false in the options array when creating
+     * a new {@link Drupal.dialog}.
+     *
+     * @function Drupal.dialog~resetSize
+     *
+     * @param {jQuery.Event} event
+     *   The event triggered.
+     *
+     * @fires event:dialogContentResize
+     */
+    return function (event) {
+      var positionOptions = ['width', 'height', 'minWidth', 'minHeight', 'maxHeight', 'maxWidth', 'position'];
+      var adjustedOptions = {};
+      var windowHeight = $(window).height();
+      var $element = event.data.$element;
+      var option;
+      var optionValue;
+      var adjustedValue;
+
+      // Take offsets in account for non-modals
+      if (!isModal) {
+        windowHeight -= displace.offsets.top + displace.offsets.bottom;
+      }
+
+      for (var n = 0; n < positionOptions.length; n++) {
+        option = positionOptions[n];
+        optionValue = event.data.settings[option];
+        if (optionValue) {
+          // jQuery UI does not support percentages on heights, convert to pixels.
+          if (typeof optionValue === 'string' && /%$/.test(optionValue) && /height/i.test(option)) {
+            adjustedValue = parseInt(0.01 * parseInt(optionValue, 10) * windowHeight, 10);
+            // Don't force the dialog to be bigger vertically than needed.
+            if (option === 'height' && $element.parent().outerHeight() < adjustedValue) {
+              adjustedValue = 'auto';
+            }
+            adjustedOptions[option] = adjustedValue;
           }
-          adjustedOptions[option] = adjustedValue;
         }
       }
+      // Offset the dialog center to be at the center of Drupal.displace.offsets.
+      if (!isModal) {
+        adjustedOptions = resetPosition(adjustedOptions);
+      }
+      // Modals don't need to take offsets into account.
+      else {
+        adjustedOptions.position = {
+          my: 'center',
+          of: window
+        };
+      }
+      $element
+        .dialog('option', adjustedOptions)
+        .trigger('dialogContentResize');
     }
-    // Offset the dialog center to be at the center of Drupal.displace.offsets.
-    adjustedOptions = resetPosition(adjustedOptions);
-    event.data.$element
-      .dialog('option', adjustedOptions)
-      .trigger('dialogContentResize');
   }
 
   /**
@@ -89,16 +111,24 @@
 
   $(window).on({
     'dialog:aftercreate': function (event, dialog, $element, settings) {
-      var autoResize = debounce(resetSize, 20);
-      var eventData = {settings: settings, $element: $element};
-      if (settings.autoResize === true || settings.autoResize === 'true') {
+      var autoResize = settings.autoResize === true || settings.autoResize === 'true';
+      if (autoResize) {
+        var autoResizeHandler = debounce(resetSize(settings.modal), 20);
+        var eventData = {settings: settings, $element: $element};
+
         $element
           .dialog('option', {resizable: false, draggable: false})
           .dialog('widget').css('position', 'fixed');
+
         $(window)
-          .on('resize.dialogResize scroll.dialogResize', eventData, autoResize)
+          .on('resize.dialogResize scroll.dialogResize', eventData, autoResizeHandler)
           .trigger('resize.dialogResize');
-        $(document).on('drupalViewportOffsetChange', eventData, autoResize);
+
+        // Modals by nature don't need to care about displace offsets. I can
+        // overlap anything.
+        if (!settings.modal) {
+          $(document).on('drupalViewportOffsetChange', eventData, autoResizeHandler);
+        }
       }
     },
     'dialog:beforeclose': function (event, dialog, $element) {