diff --git a/src/ol/source/wmssource.js b/src/ol/source/wmssource.js
index dac71c6b10..230a5a5889 100644
--- a/src/ol/source/wmssource.js
+++ b/src/ol/source/wmssource.js
@@ -95,6 +95,11 @@ ol.source.wms.getFeatureInfo =
     goog.object.extend(params, {'X': x, 'Y': y});
   }
   goog.object.extend(params, localOptions.params);
+  for (var key in params) {
+    if (goog.uri.utils.hasParam(url, key)) {
+      url = goog.uri.utils.removeParam(url, key);
+    }
+  }
   url = goog.uri.utils.appendParamsFromMap(url, params);
   if (localOptions.method == ol.source.WMSGetFeatureInfoMethod.IFRAME) {
     goog.global.setTimeout(function() {
diff --git a/test/spec/ol/source/wmssource.test.js b/test/spec/ol/source/wmssource.test.js
index fb23af0dbf..f5241abc9f 100644
--- a/test/spec/ol/source/wmssource.test.js
+++ b/test/spec/ol/source/wmssource.test.js
@@ -45,6 +45,17 @@ describe('ol.source.wms', function() {
             done();
           });
     });
+    it('overrides any existing parameters', function(done) {
+      ol.source.wms.getFeatureInfo('?REQUEST=GetMap&VERSION=1.3&LAYERS=' +
+          'foo&STYLES=x',
+          [5, 10], {params: {'INFO_FORMAT': 'text/plain', STYLES: 'y'}},
+          function(info) {
+            expect(info).to.eql('<iframe seamless src="' +
+                '?REQUEST=GetFeatureInfo&VERSION=1.3&LAYERS=foo&QUERY_LAYERS=' +
+                'foo&INFO_FORMAT=text%2Fplain&I=5&J=10&STYLES=y"></iframe>');
+            done();
+          });
+    });
   });
 
 });