diff --git a/lib/checkstl.cpp b/lib/checkstl.cpp
index 33cd61be6..e19a1846b 100644
--- a/lib/checkstl.cpp
+++ b/lib/checkstl.cpp
@@ -1937,10 +1937,10 @@ void CheckStl::string_c_str()
     }
 
     auto isString = [](const Token* str) -> bool {
+        while (Token::Match(str, "::|."))
+            str = str->astOperand2();
         if (Token::Match(str, "(|[") && !(str->valueType() && str->valueType()->type == ValueType::ITERATOR))
             str = str->previous();
-        else if (Token::simpleMatch(str, "."))
-            str = str->astOperand2();
         return str && ((str->variable() && str->variable()->isStlStringType()) || // variable
                        (str->function() && isStlStringType(str->function()->retDef)) || // function returning string
                        (str->valueType() && str->valueType()->type == ValueType::ITERATOR && isStlStringType(str->valueType()->containerTypeToken))); // iterator pointing to string
diff --git a/test/teststl.cpp b/test/teststl.cpp
index d35c2fcf1..88bdfa89d 100644
--- a/test/teststl.cpp
+++ b/test/teststl.cpp
@@ -3900,6 +3900,7 @@ private:
               "    std::string a[1];\n"
               "    struct U { std::string s; } u;"
               "};\n"
+              "namespace N { namespace O { std::string s; } }\n"
               "void g(const std::vector<std::string>& v, T& t) {\n"
               "    for (std::vector<std::string>::const_iterator it = v.begin(); it != v.end(); ++it)\n"
               "        f(it->c_str());\n"
@@ -3907,12 +3908,14 @@ private:
               "    f(t.g().c_str());\n"
               "    f(t.a[0].c_str());\n"
               "    f(t.u.s.c_str());\n"
+              "    f(N::O::s.c_str());\n"
               "}\n");
-        ASSERT_EQUALS("[test.cpp:8]: (performance) Passing the result of c_str() to a function that takes std::string as argument no. 1 is slow and redundant.\n"
-                      "[test.cpp:9]: (performance) Passing the result of c_str() to a function that takes std::string as argument no. 1 is slow and redundant.\n"
+        ASSERT_EQUALS("[test.cpp:9]: (performance) Passing the result of c_str() to a function that takes std::string as argument no. 1 is slow and redundant.\n"
                       "[test.cpp:10]: (performance) Passing the result of c_str() to a function that takes std::string as argument no. 1 is slow and redundant.\n"
                       "[test.cpp:11]: (performance) Passing the result of c_str() to a function that takes std::string as argument no. 1 is slow and redundant.\n"
-                      "[test.cpp:12]: (performance) Passing the result of c_str() to a function that takes std::string as argument no. 1 is slow and redundant.\n",
+                      "[test.cpp:12]: (performance) Passing the result of c_str() to a function that takes std::string as argument no. 1 is slow and redundant.\n"
+                      "[test.cpp:13]: (performance) Passing the result of c_str() to a function that takes std::string as argument no. 1 is slow and redundant.\n"
+                      "[test.cpp:14]: (performance) Passing the result of c_str() to a function that takes std::string as argument no. 1 is slow and redundant.\n",
                       errout.str());
 
         check("void svgFile(const std::string &content, const std::string &fileName, const double end = 1000., const double start = 0.);\n"