diff --git a/js/modal.js b/js/modal.js
index c757ef2..72bdc79 100644
--- a/js/modal.js
+++ b/js/modal.js
@@ -303,6 +303,7 @@
 
     if ($('#modal-content').hasClass('ctools-modal-loading')) {
       $('#modal-content').removeClass('ctools-modal-loading');
+      modalContentResize();
     }
     else {
       // If the modal was already shown, and we are simply replacing its
@@ -311,6 +312,43 @@
       // button by the show() function called above.)
       $('#modal-content :focusable:first').focus();
     }
+
+    // Trigger a window resize after a delay to ensure that the modal is
+    // centered properly.
+    // See https://www.drupal.org/node/1803104
+    Drupal.CTools.Modal.center_modal();
+
+  }
+
+  /**
+   * Ensure modal is centered.
+   */
+  Drupal.CTools.Modal.center_modal = function() {
+    // If the modal doesn't exist, bail.
+    var $modal_content = $('#modalContent');
+    if ($modal_content.length === 0) {
+      return;
+    }
+    // Get the middle of the window.
+    var windowCenter =  $(window).width() / 2;
+    // Get left, width, and center of the modal.
+    var modalLeft = $modal_content.offset().left;
+    var modalWidth = $modal_content.width();
+    var modalCenter = modalLeft + modalWidth / 2;
+    // Check to see how far off the modal and window middles are.
+    var diff = windowCenter - modalCenter;
+    // Consider the modal not centered if it has a width less than 10, or if
+    // its left edge is not at zero and the difference between the window
+    // center and the modal center is greater than |1| (we allow a difference
+    // of 1 positive and negative in case division result a float).
+    if (modalWidth < 10 || (modalLeft > 0 && (diff > 1 || diff < -1))) {
+      // Modal is not centered. Trigger resize to force modal to center and
+      // wait 10 ms before retrying.
+      $(window).trigger('resize').delay(10).queue(function(){
+        $(this).dequeue();
+        Drupal.CTools.Modal.center_modal();
+      });
+    }
   }
 
   /**
@@ -633,7 +671,8 @@
 
       // Apply the changes
       $('#modalBackdrop').css('height', docHeight + 'px').css('width', docWidth + 'px').show();
-      modalContent.css('top', mdcTop + 'px').css('left', mdcLeft + 'px').show();
+      var topPx = mdcTop < 0 ? 0 : mdcTop;
+      modalContent.css('top', topPx + 'px').css('left', mdcLeft + 'px').show();
     };
     $(window).bind('resize', modalContentResize);
   };