diff --git a/python/src/com/jetbrains/python/inspections/unresolvedReference/PyUnresolvedReferencesInspection.java b/python/src/com/jetbrains/python/inspections/unresolvedReference/PyUnresolvedReferencesInspection.java
index 6f48759c674f..746812997858 100644
--- a/python/src/com/jetbrains/python/inspections/unresolvedReference/PyUnresolvedReferencesInspection.java
+++ b/python/src/com/jetbrains/python/inspections/unresolvedReference/PyUnresolvedReferencesInspection.java
@@ -1,18 +1,4 @@
-/*
- * Copyright 2000-2017 JetBrains s.r.o.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
+// Copyright 2000-2017 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
 package com.jetbrains.python.inspections.unresolvedReference;
 
 import com.google.common.collect.ImmutableSet;
@@ -799,6 +785,9 @@ public class PyUnresolvedReferencesInspection extends PyInspection {
           return true;
         }
       }
+      if (type instanceof PyUnionType) {
+        return ContainerUtil.exists(((PyUnionType)type).getMembers(), member -> ignoreUnresolvedMemberForType(member, reference, name));
+      }
       for (PyInspectionExtension extension : Extensions.getExtensions(PyInspectionExtension.EP_NAME)) {
         if (extension.ignoreUnresolvedMember(type, name, myTypeEvalContext)) {
           return true;
diff --git a/python/testData/inspections/PyUnresolvedReferencesInspection/unionContainingUnknownType.py b/python/testData/inspections/PyUnresolvedReferencesInspection/unionContainingUnknownType.py
new file mode 100644
index 000000000000..46553e364fee
--- /dev/null
+++ b/python/testData/inspections/PyUnresolvedReferencesInspection/unionContainingUnknownType.py
@@ -0,0 +1,4 @@
+def foo(smth, param):
+    if smth:
+        param = ""
+    print(param.smth())
\ No newline at end of file
diff --git a/python/testSrc/com/jetbrains/python/inspections/PyUnresolvedReferencesInspectionTest.java b/python/testSrc/com/jetbrains/python/inspections/PyUnresolvedReferencesInspectionTest.java
index 07c979683ee6..e5bd5d9d95d9 100644
--- a/python/testSrc/com/jetbrains/python/inspections/PyUnresolvedReferencesInspectionTest.java
+++ b/python/testSrc/com/jetbrains/python/inspections/PyUnresolvedReferencesInspectionTest.java
@@ -1,18 +1,4 @@
-/*
- * Copyright 2000-2017 JetBrains s.r.o.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
+// Copyright 2000-2017 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
 package com.jetbrains.python.inspections;
 
 import com.intellij.codeInsight.intention.IntentionAction;
@@ -652,6 +638,11 @@ public class PyUnresolvedReferencesInspectionTest extends PyInspectionTestCase {
     doTest();
   }
 
+  // PY-22312
+  public void testUnionContainingUnknownType() {
+    doTest();
+  }
+
   @NotNull
   @Override
   protected Class<? extends PyInspection> getInspectionClass() {