diff --git a/lib/executionpath.cpp b/lib/executionpath.cpp
index 8b9f35cae..dda101cc6 100644
--- a/lib/executionpath.cpp
+++ b/lib/executionpath.cpp
@@ -145,6 +145,11 @@ void ExecutionPath::checkScope(const Token *tok, std::list<ExecutionPath *> &che
             return;
         }
 
+        if (Token::simpleMatch(tok, "union {")) {
+            tok = tok->next()->link();
+            continue;
+        }
+
         if (tok->str() == "}")
             return;
 
diff --git a/test/testuninitvar.cpp b/test/testuninitvar.cpp
index e56fe9527..6be444e87 100644
--- a/test/testuninitvar.cpp
+++ b/test/testuninitvar.cpp
@@ -558,6 +558,22 @@ private:
                        "  return Range;\n"
                        "}\n");
         ASSERT_EQUALS("", errout.str());
+
+        // #4040 - False positive
+        checkUninitVar("int f(int x)  {\n"
+                       "    int iter;\n"
+                       "    {\n"
+                       "        union\n"
+                       "        {\n"
+                       "            int asInt;\n"
+                       "            double asDouble;\n"
+                       "        };\n"
+                       "\n"
+                       "        iter = x;\n"
+                       "    }\n"
+                       "    return 1 + iter;\n"
+                       "}");
+        ASSERT_EQUALS("", errout.str());
     }
 
     void uninitvar3() { // #3844