diff --git a/lib/jekyll-maps/google_map_api.js b/lib/jekyll-maps/google_map_api.js
index d9564b8..58126e2 100644
--- a/lib/jekyll-maps/google_map_api.js
+++ b/lib/jekyll-maps/google_map_api.js
@@ -80,7 +80,7 @@ var jekyllMaps = (function() {
         title: location.title,
         image: location.image,
         icon: location.icon || mapOptions.markerIcon,
-        url: location.url.length > 0 ? mapOptions.baseUrl + location.url : '',
+        url: markerUrl(mapOptions.baseUrl, location.url),
         map: map
       })
       if (mapOptions.showMarkerPopup) marker.addListener('click', markerPopup)
@@ -88,6 +88,12 @@ var jekyllMaps = (function() {
       return marker
     }
 
+    function markerUrl(baseUrl, url) {
+      if (/^(https?|\/\/)/.test(url)) return url
+
+      return url.length > 0 ? baseUrl + url : ''
+    }
+
     function markerPopup() {
       var contentHtml =
         '<div class="map-info-window"><h5>' + this.title + '</h5>'