diff --git a/lib/checkstl.cpp b/lib/checkstl.cpp
index ebeb7f44f..15bf0ac70 100644
--- a/lib/checkstl.cpp
+++ b/lib/checkstl.cpp
@@ -2430,19 +2430,28 @@ void CheckStl::localMutexError(const Token* tok)
 void CheckStl::checkMutexes()
 {
     for (const Scope *function : mTokenizer->getSymbolDatabase()->functionScopes) {
+        std::set<nonneg int> checkedVars;
         for (const Token *tok = function->bodyStart; tok != function->bodyEnd; tok = tok->next()) {
+            if (!Token::Match(tok, "%var%"))
+                continue;
             const Variable* var = tok->variable();
             if (!var)
                 continue;
             if (Token::Match(tok, "%var% . lock ( )")) {
                 if (!isMutex(var))
                     continue;
+                if (!checkedVars.insert(var->declarationId()).second)
+                    continue;
                 if (isLocalMutex(var, tok->scope()))
                     localMutexError(tok);
             } else if (Token::Match(tok, "%var% (|{ %var% )|}|,")) {
                 if (!isLockGuard(var))
                     continue;
                 const Variable* mvar = tok->tokAt(2)->variable();
+                if (!mvar)
+                    continue;
+                if (!checkedVars.insert(mvar->declarationId()).second)
+                    continue;
                 if (var->isStatic() || var->isGlobal())
                     globalLockGuardError(tok);
                 else if (isLocalMutex(mvar, tok->scope()))
diff --git a/test/teststl.cpp b/test/teststl.cpp
index 240e20709..931fdc73f 100644
--- a/test/teststl.cpp
+++ b/test/teststl.cpp
@@ -4554,6 +4554,36 @@ private:
               "}\n",
               true);
         ASSERT_EQUALS("[test.cpp:5]: (warning) The lock is ineffective because the mutex is locked at the same scope as the mutex itself.\n", errout.str());
+
+        check("void foo();\n"
+              "void bar();\n"
+              "void f() {\n"
+              "    std::mutex m;\n"
+              "    std::thread t([&m](){\n"
+              "        m.lock();\n"
+              "        foo();\n"
+              "        m.unlock();\n"
+              "    });\n"
+              "    m.lock();\n"
+              "    bar();\n"
+              "    m.unlock();\n"
+              "}\n",
+              true);
+        ASSERT_EQUALS("", errout.str());
+
+        check("void foo();\n"
+              "void bar();\n"
+              "void f() {\n"
+              "    std::mutex m;\n"
+              "    std::thread t([&m](){\n"
+              "        std::unique_lock<std::mutex> g{m};\n"
+              "        foo();\n"
+              "    });\n"
+              "    std::unique_lock<std::mutex> g{m};\n"
+              "    bar();\n"
+              "}\n",
+              true);
+        ASSERT_EQUALS("", errout.str());
     }
 };