diff --git a/examples/wms-image-custom-proj.js b/examples/wms-image-custom-proj.js
index 4548247b84..c916a16df5 100644
--- a/examples/wms-image-custom-proj.js
+++ b/examples/wms-image-custom-proj.js
@@ -28,7 +28,7 @@ var layers = [
         'LAYERS': 'ch.swisstopo.pixelkarte-farbe-pk1000.noscale',
         'FORMAT': 'image/jpeg'
       },
-      serverType: 'mapserver',
+      serverType: /** @type {ol.source.wms.ServerType} */ ('mapserver'),
       extent: extent
     })
   }),
@@ -43,7 +43,7 @@ var layers = [
             'National parks / geo.admin.ch</a>'
       })],
       params: {'LAYERS': 'ch.bafu.schutzgebiete-paerke_nationaler_bedeutung'},
-      serverType: 'mapserver',
+      serverType: /** @type {ol.source.wms.ServerType} */ ('mapserver'),
       extent: extent
     })
   })
diff --git a/examples/wms-image.js b/examples/wms-image.js
index dd495aac46..1e25cb53e2 100644
--- a/examples/wms-image.js
+++ b/examples/wms-image.js
@@ -15,7 +15,7 @@ var layers = [
     source: new ol.source.ImageWMS({
       url: 'http://demo.opengeo.org/geoserver/wms',
       params: {'LAYERS': 'topp:states'},
-      serverType: 'geoserver',
+      serverType: /** @type {ol.source.wms.ServerType} */ ('geoserver'),
       extent: [-13884991, 2870341, -7455066, 6338219]
     })
   })
diff --git a/examples/wms-no-proj.js b/examples/wms-no-proj.js
index 260961b6b6..545b16a464 100644
--- a/examples/wms-no-proj.js
+++ b/examples/wms-no-proj.js
@@ -37,7 +37,7 @@ var layers = [
       })],
       crossOrigin: 'anonymous',
       params: {'LAYERS': 'ch.bafu.schutzgebiete-paerke_nationaler_bedeutung'},
-      serverType: 'mapserver',
+      serverType: /** @type {ol.source.wms.ServerType} */ ('mapserver'),
       url: 'http://wms.geo.admin.ch/'
     })
   })