diff --git a/docs/changes.rst b/docs/changes.rst
index e3c118a0..e1482f12 100644
--- a/docs/changes.rst
+++ b/docs/changes.rst
@@ -30,6 +30,9 @@ Released: not yet
 
 * Pinned version of colorama to <0.4.0 for Python <=3.4.
 
+* Adjusted to changes in the pywbem mock support for method providers, in the
+  sample method provider simple_mock_invokemethod_pywbem_V1.py. (See issue #646)
+
 **Enhancements:**
 
 * Enabled installation using 'setup.py install' from unpacked source distribution
diff --git a/tests/unit/simple_mock_invokemethod_pywbem_V1.py b/tests/unit/simple_mock_invokemethod_pywbem_V1.py
index 63913dc1..852f8523 100644
--- a/tests/unit/simple_mock_invokemethod_pywbem_V1.py
+++ b/tests/unit/simple_mock_invokemethod_pywbem_V1.py
@@ -59,14 +59,13 @@ def InvokeMethod(self, namespace, MethodName, ObjectName, Params):
 
         if isinstance(ObjectName, CIMInstanceName):
             instance_store = self.cimrepository.get_instance_store(namespace)
-            inst = self.find_instance(ObjectName, instance_store, copy=False)
-            if inst is None:
+            if not instance_store.object_exists(ObjectName):
                 raise CIMError(
                     CIM_ERR_NOT_FOUND,
-                    "Instance {0} does not exist in CIM repository, "
-                    "namespace {1}".format(ObjectName, namespace))
-        # This method expects a single parameter input
+                    "Instance {0} does not exist in CIM repository",
+                    format(ObjectName))
 
+        # This method expects a single parameter input
         return_params = []
         if MethodName.lower() == 'fuzzy':
             if Params: