diff --git a/contribs/gmf/src/directives/print.js b/contribs/gmf/src/directives/print.js
index c811727caaf7..f2ec5e9484d7 100644
--- a/contribs/gmf/src/directives/print.js
+++ b/contribs/gmf/src/directives/print.js
@@ -698,6 +698,7 @@ gmf.PrintController.prototype.print = function(format) {
           layer = this.ngeoLayerHelper_.createBasicWMSLayer(
             server.url,
             layer_names,
+            server.imageType,
             server.type
           );
         } else {
diff --git a/contribs/gmf/src/services/syncLayertreeMap.js b/contribs/gmf/src/services/syncLayertreeMap.js
index fa95a030c82d..8d84cd9c5c5d 100644
--- a/contribs/gmf/src/services/syncLayertreeMap.js
+++ b/contribs/gmf/src/services/syncLayertreeMap.js
@@ -197,8 +197,9 @@ gmf.SyncLayertreeMap.prototype.createLayerFromGroup_ = function(treeCtrl,
     goog.asserts.assert(ogcServer);
     goog.asserts.assert(ogcServer.url);
     goog.asserts.assert(ogcServer.type);
+    goog.asserts.assert(ogcServer.imageType);
     layer = this.layerHelper_.createBasicWMSLayer(
-        ogcServer.url, '', ogcServer.type, timeParam
+        ogcServer.url, '', ogcServer.imageType, ogcServer.type, timeParam
     );
     var hasActiveChildren = false;
     treeCtrl.traverseDepthFirst(function(ctrl) {
@@ -238,8 +239,9 @@ gmf.SyncLayertreeMap.prototype.createLeafInAMixedGroup_ = function(treeCtrl, map
     goog.asserts.assert(ogcServer.url);
     goog.asserts.assert(ogcServer.type);
     goog.asserts.assert(gmfLayerWMS.layers);
+    goog.asserts.assert(ogcServer.imageType);
     layer = this.layerHelper_.createBasicWMSLayer(ogcServer.url,
-            gmfLayerWMS.layers, ogcServer.type, timeParam);
+            gmfLayerWMS.layers, ogcServer.imageType, ogcServer.type, timeParam);
   }
   // Update layer information and tree state.
   layer.set('layerNodeName', gmfLayer.name); // Really useful ?
diff --git a/contribs/gmf/src/services/themesservice.js b/contribs/gmf/src/services/themesservice.js
index 0ea9d6423ef9..1e5b6677a29d 100644
--- a/contribs/gmf/src/services/themesservice.js
+++ b/contribs/gmf/src/services/themesservice.js
@@ -289,9 +289,11 @@ gmf.Themes.prototype.getBgLayers = function(appDimensions) {
       var server = ogcServers[gmfLayerWMS.ogcServer];
       goog.asserts.assert(server, 'The OGC server was not found');
       goog.asserts.assert(server.url, 'The server URL is required');
+      goog.asserts.assert(server.imageType, 'The server image type is required');
       return callback(gmfLayer, layerHelper.createBasicWMSLayer(
           server.url,
           gmfLayerWMS.layers || '',
+          server.imageType,
           server.type,
           undefined, // time
           gmfLayer.dimensions
diff --git a/src/services/layerHelper.js b/src/services/layerHelper.js
index 73fc6abc19a0..986af30b0d1b 100644
--- a/src/services/layerHelper.js
+++ b/src/services/layerHelper.js
@@ -57,6 +57,7 @@ ngeo.LayerHelper.REFRESH_PARAM = 'random';
  *
  * @param {string} sourceURL The source URL.
  * @param {string} sourceLayersName A comma separated names string.
+ * @param {string} sourceFormat Image format, for example 'image/png'.
  * @param {string=} opt_serverType Type of the server ("mapserver",
  *     "geoserver", "qgisserver", …).
  * @param {string=} opt_time time parameter for layer queryable by time/periode
@@ -65,9 +66,12 @@ ngeo.LayerHelper.REFRESH_PARAM = 'random';
  * @export
  */
 ngeo.LayerHelper.prototype.createBasicWMSLayer = function(sourceURL,
-    sourceLayersName, opt_serverType, opt_time, opt_params) {
+    sourceLayersName, sourceFormat, opt_serverType, opt_time, opt_params) {
 
-  var params = {'LAYERS': sourceLayersName};
+  var params = {
+    'FORMAT': sourceFormat,
+    'LAYERS': sourceLayersName
+  };
   var olServerType;
   if (opt_time) {
     params['TIME'] = opt_time;
diff --git a/test/spec/services/layerHelper.spec.js b/test/spec/services/layerHelper.spec.js
index 75a0f7d43ea2..07d3ebcc78af 100644
--- a/test/spec/services/layerHelper.spec.js
+++ b/test/spec/services/layerHelper.spec.js
@@ -23,9 +23,14 @@ describe('ngeo.LayerHelper', function() {
   });
 
   it('Create a basic WMS layer', function() {
-    layer = ngeoLayerHelper.createBasicWMSLayer('', '');
+    layer = ngeoLayerHelper.createBasicWMSLayer('http://example.com/', 'a,b,c', 'image/jpeg');
     expect(layer.constructor).toBe(ol.layer.Image);
-    expect(layer.getSource().constructor).toBe(ol.source.ImageWMS);
+    var source = layer.getSource();
+    expect(source.constructor).toBe(ol.source.ImageWMS);
+    expect(source.getUrl()).toBe('http://example.com/');
+    var params = source.getParams();
+    expect(params.LAYERS).toBe('a,b,c');
+    expect(params.FORMAT).toBe('image/jpeg');
   });
 
   it('Create a WMTS layer from capabilitites', function() {