diff --git a/src/providers/wfs/qgswfsdatasourceuri.cpp b/src/providers/wfs/qgswfsdatasourceuri.cpp
index 21c527c2d5d9..5718065b633c 100644
--- a/src/providers/wfs/qgswfsdatasourceuri.cpp
+++ b/src/providers/wfs/qgswfsdatasourceuri.cpp
@@ -202,11 +202,18 @@ QUrl QgsWFSDataSourceURI::requestUrl( const QString &request, const Method &meth
         // One could argue that the server should expose them in the DCP endpoint.
         url = QUrl( mGetEndpoints[ request ] );
         urlQuery = QUrlQuery( url );
+        // OGC case insensitive keys KVP: see https://github.com/qgis/QGIS/issues/34148
+        QSet<QString> upperCaseQueryItemKeys;
+        const QList<QPair<QString, QString>> constQueryItems { urlQuery.queryItems() };
+        for ( const auto &qi : constQueryItems )
+        {
+          upperCaseQueryItemKeys.insert( qi.first.toUpper() );
+        }
         const QUrlQuery defaultUrlQuery( defaultUrl );
         const auto itemsDefaultUrl( defaultUrlQuery.queryItems() );
         for ( const auto &item : itemsDefaultUrl )
         {
-          if ( !urlQuery.hasQueryItem( item.first ) )
+          if ( !upperCaseQueryItemKeys.contains( item.first.toUpper() ) )
           {
             urlQuery.addQueryItem( item.first, item.second );
           }
diff --git a/tests/src/python/test_provider_wfs.py b/tests/src/python/test_provider_wfs.py
index fbaef1baf40c..3f348d5eb7db 100644
--- a/tests/src/python/test_provider_wfs.py
+++ b/tests/src/python/test_provider_wfs.py
@@ -4258,6 +4258,81 @@ def do_GET(self):
         errors = vl.dataProvider().errors()
         self.assertEqual(len(errors), 0, errors)
 
+    def testWFS20CaseInsensitiveKVP(self):
+        """Test an URL with non standard query string arguments where the server exposes
+        the same parameters with different case: see https://github.com/qgis/QGIS/issues/34148
+        """
+        endpoint = self.__class__.basetestpath + '/fake_qgis_http_endpoint_WFS_case_insensitive_kvp_2.0'
+
+        get_cap = """
+<WFS_Capabilities version="1.0.0" xmlns="http://www.opengis.net/wfs" xmlns:ogc="http://www.opengis.net/ogc">
+  <FeatureTypeList>
+    <FeatureType>
+      <Name>my:typename</Name>
+      <Title>Title</Title>
+      <Abstract>Abstract</Abstract>
+      <SRS>EPSG:32631</SRS>
+      <!-- in WFS 1.0, LatLongBoundingBox is in SRS units, not necessarily lat/long... -->
+      <LatLongBoundingBox minx="400000" miny="5400000" maxx="450000" maxy="5500000"/>
+    </FeatureType>
+  </FeatureTypeList>
+  <OperationsMetadata>
+    <Operation name="DescribeFeatureType">
+      <DCP>
+        <HTTP>
+          <Get type="simple" href="http://{0}?PARAMETER1=Value1&amp;PARAMETER2=Value2&amp;"/>
+          <Post type="simple" href="http://{0}?PARAMETER1=Value1&amp;PARAMETER2=Value2&amp;"/>
+        </HTTP>
+      </DCP>
+    </Operation>
+    <Operation name="GetFeature">
+      <DCP>
+        <HTTP>
+          <Get type="simple" href="http://{0}?PARAMETER1=Value1&amp;PARAMETER2=Value2&amp;"/>
+          <Post type="simple" href="http://{0}?PARAMETER1=Value1&amp;PARAMETER2=Value2&amp;"/>
+        </HTTP>
+      </DCP>
+    </Operation>
+  </OperationsMetadata></WFS_Capabilities>""".format(endpoint).encode('UTF-8')
+
+        with open(sanitize(endpoint, '?PARAMETER1=Value1&PARAMETER2=Value2&FOO=BAR&SERVICE=WFS&REQUEST=GetCapabilities&VERSION=1.0.0'), 'wb') as f:
+            f.write(get_cap)
+
+        with open(sanitize(endpoint, '?Parameter1=Value1&Parameter2=Value2&FOO=BAR&SERVICE=WFS&REQUEST=GetCapabilities&VERSION=1.0.0'), 'wb') as f:
+            f.write(get_cap)
+
+        with open(sanitize(endpoint, '?PARAMETER1=Value1&PARAMETER2=Value2&FOO=BAR&SERVICE=WFS&REQUEST=DescribeFeatureType&VERSION=1.0.0&TYPENAME=my:typename'), 'wb') as f:
+            f.write("""
+<xsd:schema xmlns:my="http://my" xmlns:gml="http://www.opengis.net/gml" xmlns:xsd="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified" targetNamespace="http://my">
+  <xsd:import namespace="http://www.opengis.net/gml"/>
+  <xsd:complexType name="typenameType">
+    <xsd:complexContent>
+      <xsd:extension base="gml:AbstractFeatureType">
+        <xsd:sequence>
+          <xsd:element maxOccurs="1" minOccurs="0" name="INTFIELD" nillable="true" type="xsd:int"/>
+          <xsd:element maxOccurs="1" minOccurs="0" name="GEOMETRY" nillable="true" type="xsd:int"/>
+          <xsd:element maxOccurs="1" minOccurs="0" name="longfield" nillable="true" type="xsd:long"/>
+          <xsd:element maxOccurs="1" minOccurs="0" name="stringfield" nillable="true" type="xsd:string"/>
+          <xsd:element maxOccurs="1" minOccurs="0" name="datetimefield" nillable="true" type="xsd:dateTime"/>
+          <!-- use geometry that is the default SpatiaLite geometry name -->
+          <xsd:element maxOccurs="1" minOccurs="0" name="geometry" nillable="true" type="gml:PointPropertyType"/>
+        </xsd:sequence>
+      </xsd:extension>
+    </xsd:complexContent>
+  </xsd:complexType>
+  <xsd:element name="typename" substitutionGroup="gml:_Feature" type="my:typenameType"/>
+</xsd:schema>
+""".encode('UTF-8'))
+
+        vl = QgsVectorLayer("url='http://" + endpoint + "?Parameter1=Value1&Parameter2=Value2&FOO=BAR&SERVICE=WFS&REQUEST=GetCapabilities&VERSION=1.1.0" + "' typename='my:typename' version='1.0.0'", 'test', 'WFS')
+        self.assertTrue(vl.isValid())
+        self.assertEqual(vl.wkbType(), QgsWkbTypes.Point)
+        self.assertEqual(len(vl.fields()), 5)
+        self.assertEqual(vl.featureCount(), 0)
+        reference = QgsGeometry.fromRect(QgsRectangle(400000.0, 5400000.0, 450000.0, 5500000.0))
+        vl_extent = QgsGeometry.fromRect(vl.extent())
+        assert QgsGeometry.compare(vl_extent.asPolygon()[0], reference.asPolygon()[0], 0.00001), 'Expected {}, got {}'.format(reference.asWkt(), vl_extent.asWkt())
+
 
 if __name__ == '__main__':
     unittest.main()