diff --git a/lib/preprocessor.cpp b/lib/preprocessor.cpp
index 35ffc1068..a5e97b205 100644
--- a/lib/preprocessor.cpp
+++ b/lib/preprocessor.cpp
@@ -123,10 +123,18 @@ static std::string unify(const std::string &s, char separator)
 }
 
 
+bool Preprocessor::cplusplus(const Settings *settings, const std::string &filename)
+{
+    const bool undef   = settings && settings->userUndefs.find("__cplusplus") != settings->userUndefs.end();
+    const bool cpplang = settings && settings->enforcedLang == Settings::CPP;
+    const bool cppfile = (!settings || settings->enforcedLang == Settings::None) && Path::isCPP(filename);
+    return (!undef && (cpplang || cppfile));
+}
+
 /**
  * Get cfgmap - a map of macro names and values
  */
-static std::map<std::string,std::string> getcfgmap(const std::string &cfg)
+static std::map<std::string,std::string> getcfgmap(const std::string &cfg, const Settings *settings, const std::string &filename)
 {
     std::map<std::string, std::string> cfgmap;
 
@@ -154,6 +162,9 @@ static std::map<std::string,std::string> getcfgmap(const std::string &cfg)
         }
     }
 
+    if (cfgmap.find("__cplusplus") == cfgmap.end() && Preprocessor::cplusplus(settings,filename))
+        cfgmap["__cplusplus"] = "1";
+
     return cfgmap;
 }
 
@@ -1023,7 +1034,7 @@ void Preprocessor::preprocess(std::istream &srcCodeStream, std::string &processe
         processedFile = ostr.str();
     }
 
-    std::map<std::string, std::string> defs(getcfgmap(_settings ? _settings->userDefines : std::string("")));
+    std::map<std::string, std::string> defs(getcfgmap(_settings ? _settings->userDefines : std::string(""), _settings, filename));
 
     if (_settings && _settings->_maxConfigs == 1U) {
         std::set<std::string> pragmaOnce;
@@ -1735,9 +1746,7 @@ std::string Preprocessor::getcode(const std::string &filedata, const std::string
     std::list<bool> matched_ifdef;
 
     // Create a map for the cfg for faster access to defines
-    std::map<std::string, std::string> cfgmap(getcfgmap(cfg));
-    if (((_settings && _settings->enforcedLang == Settings::CPP) || ((!_settings || _settings->enforcedLang == Settings::None) && Path::isCPP(filename))) && cfgmap.find("__cplusplus") == cfgmap.end())
-        cfgmap["__cplusplus"] = "1";
+    std::map<std::string, std::string> cfgmap(getcfgmap(cfg, _settings, filename));
 
     std::stack<std::string> filenames;
     filenames.push(filename);
@@ -2895,7 +2904,7 @@ std::string Preprocessor::expandMacros(const std::string &code, std::string file
 
     {
         // fill up "macros" with user defined macros
-        const std::map<std::string,std::string> cfgmap(getcfgmap(cfg));
+        const std::map<std::string,std::string> cfgmap(getcfgmap(cfg,NULL,""));
         std::map<std::string, std::string>::const_iterator it;
         for (it = cfgmap.begin(); it != cfgmap.end(); ++it) {
             std::string s = it->first;
diff --git a/lib/preprocessor.h b/lib/preprocessor.h
index 8d944ce52..6c421a488 100644
--- a/lib/preprocessor.h
+++ b/lib/preprocessor.h
@@ -96,6 +96,9 @@ public:
     /** read preprocessor statements into a string. */
     std::string readpreprocessor(std::istream &istr, const unsigned int bom) const;
 
+    /** should __cplusplus be defined? */
+    static bool cplusplus(const Settings *settings, const std::string &filename);
+
     /**
      * Get preprocessed code for a given configuration
      * @param filedata file data including preprocessing 'if', 'define', etc
diff --git a/test/testpreprocessor.cpp b/test/testpreprocessor.cpp
index bb50bc381..f68863f90 100644
--- a/test/testpreprocessor.cpp
+++ b/test/testpreprocessor.cpp
@@ -3272,11 +3272,21 @@ private:
         ASSERT_EQUALS("char buf[$123];\n", actual);
     }
 
-    void predefine5() {  // #3737 - automatically define __cplusplus
+    void predefine5() {  // #3737, #5119 - automatically define __cplusplus
+        // #3737...
         const char code[] = "#ifdef __cplusplus\n123\n#endif";
         Preprocessor preprocessor(NULL,this);
         ASSERT_EQUALS("\n\n\n",    preprocessor.getcode(code, "X=123", "test.c"));
         ASSERT_EQUALS("\n123\n\n", preprocessor.getcode(code, "X=123", "test.cpp"));
+
+        // #5119...
+        ASSERT_EQUALS(false, Preprocessor::cplusplus(NULL,"test.c"));
+        ASSERT_EQUALS(true, Preprocessor::cplusplus(NULL,"test.cpp"));
+
+        Settings settings;
+        ASSERT_EQUALS(true, Preprocessor::cplusplus(&settings,"test.cpp"));
+        settings.userUndefs.insert("__cplusplus");
+        ASSERT_EQUALS(false, Preprocessor::cplusplus(&settings,"test.cpp"));
     }
 
     void predefine6() {  // #3737 - using -D and -f => check all matching configurations