diff --git a/externals/simplecpp/simplecpp.cpp b/externals/simplecpp/simplecpp.cpp
index 47bb78f8cf17..3cce780efcad 100755
--- a/externals/simplecpp/simplecpp.cpp
+++ b/externals/simplecpp/simplecpp.cpp
@@ -22,6 +22,7 @@
 #include <exception>
 #include <fstream>
 #include <iostream>
+#include <istream>
 #include <limits>
 #include <list>
 #include <map>
@@ -377,6 +378,42 @@ class StdIStream : public simplecpp::TokenList::Stream {
     std::istream &istr;
 };
 
+class StdCharBufStream : public simplecpp::TokenList::Stream {
+public:
+    // cppcheck-suppress uninitDerivedMemberVar - we call Stream::init() to initialize the private members
+    StdCharBufStream(const unsigned char* str, std::size_t size)
+        : str(str)
+        , size(size)
+        , pos(0)
+        , lastStatus(0)
+    {
+        init();
+    }
+
+    virtual int get() OVERRIDE {
+        if (pos >= size)
+            return lastStatus = EOF;
+        return str[pos++];
+    }
+    virtual int peek() OVERRIDE {
+        if (pos >= size)
+            return lastStatus = EOF;
+        return str[pos];
+    }
+    virtual void unget() OVERRIDE {
+        --pos;
+    }
+    virtual bool good() OVERRIDE {
+        return lastStatus != EOF;
+    }
+
+private:
+    const unsigned char *str;
+    const std::size_t size;
+    std::size_t pos;
+    int lastStatus;
+};
+
 class FileStream : public simplecpp::TokenList::Stream {
 public:
     // cppcheck-suppress uninitDerivedMemberVar - we call Stream::init() to initialize the private members
@@ -442,6 +479,20 @@ simplecpp::TokenList::TokenList(std::istream &istr, std::vector<std::string> &fi
     readfile(stream,filename,outputList);
 }
 
+simplecpp::TokenList::TokenList(const unsigned char* data, std::size_t size, std::vector<std::string> &filenames, const std::string &filename, OutputList *outputList)
+    : frontToken(nullptr), backToken(nullptr), files(filenames)
+{
+    StdCharBufStream stream(data, size);
+    readfile(stream,filename,outputList);
+}
+
+simplecpp::TokenList::TokenList(const char* data, std::size_t size, std::vector<std::string> &filenames, const std::string &filename, OutputList *outputList)
+        : frontToken(nullptr), backToken(nullptr), files(filenames)
+{
+    StdCharBufStream stream(reinterpret_cast<const unsigned char*>(data), size);
+    readfile(stream,filename,outputList);
+}
+
 simplecpp::TokenList::TokenList(const std::string &filename, std::vector<std::string> &filenames, OutputList *outputList)
         : frontToken(nullptr), backToken(nullptr), files(filenames)
 {
@@ -1447,8 +1498,7 @@ namespace simplecpp {
 
         Macro(const std::string &name, const std::string &value, std::vector<std::string> &f) : nameTokDef(nullptr), files(f), tokenListDefine(f), valueDefinedInCode_(false) {
             const std::string def(name + ' ' + value);
-            std::istringstream istr(def);
-            StdIStream stream(istr);
+            StdCharBufStream stream(reinterpret_cast<const unsigned char*>(def.data()), def.size());
             tokenListDefine.readfile(stream);
             if (!parseDefine(tokenListDefine.cfront()))
                 throw std::runtime_error("bad macro syntax. macroname=" + name + " value=" + value);
@@ -3315,8 +3365,17 @@ void simplecpp::preprocess(simplecpp::TokenList &output, const simplecpp::TokenL
             macros.insert(std::make_pair("__STDC_VERSION__", Macro("__STDC_VERSION__", std_def, dummy)));
         } else {
             std_def = simplecpp::getCppStdString(dui.std);
-            if (!std_def.empty())
-                macros.insert(std::make_pair("__cplusplus", Macro("__cplusplus", std_def, dummy)));
+            if (std_def.empty()) {
+                if (outputList) {
+                    simplecpp::Output err(files);
+                    err.type = Output::DUI_ERROR;
+                    err.msg = "unknown standard specified: '" + dui.std + "'";
+                    outputList->push_back(err);
+                }
+                output.clear();
+                return;
+            }
+            macros.insert(std::make_pair("__cplusplus", Macro("__cplusplus", std_def, dummy)));
         }
     }
 
@@ -3463,7 +3522,8 @@ void simplecpp::preprocess(simplecpp::TokenList &output, const simplecpp::TokenL
                     std::ifstream f;
                     header2 = openHeader(f, dui, rawtok->location.file(), header, systemheader);
                     if (f.is_open()) {
-                        TokenList * const tokens = new TokenList(f, files, header2, outputList);
+                        f.close();
+                        TokenList * const tokens = new TokenList(header2, files, outputList);
                         if (dui.removeComments)
                             tokens->removeComments();
                         filedata[header2] = tokens;
diff --git a/externals/simplecpp/simplecpp.h b/externals/simplecpp/simplecpp.h
index c72e4c655cf5..88a140145677 100755
--- a/externals/simplecpp/simplecpp.h
+++ b/externals/simplecpp/simplecpp.h
@@ -1,4 +1,4 @@
-/*
+/* -*- C++ -*-
  * simplecpp - A simple and high-fidelity C/C++ preprocessor library
  * Copyright (C) 2016-2023 simplecpp team
  */
@@ -8,7 +8,7 @@
 
 #include <cctype>
 #include <cstring>
-#include <istream>
+#include <iosfwd>
 #include <list>
 #include <map>
 #include <set>
@@ -181,7 +181,8 @@ namespace simplecpp {
             PORTABILITY_BACKSLASH,
             UNHANDLED_CHAR_ERROR,
             EXPLICIT_INCLUDE_NOT_FOUND,
-            FILE_NOT_FOUND
+            FILE_NOT_FOUND,
+            DUI_ERROR
         } type;
         explicit Output(const std::vector<std::string>& files, Type type, const std::string& msg) : type(type), location(files), msg(msg) {}
         Location location;
@@ -198,6 +199,10 @@ namespace simplecpp {
         explicit TokenList(std::vector<std::string> &filenames);
         /** generates a token list from the given std::istream parameter */
         TokenList(std::istream &istr, std::vector<std::string> &filenames, const std::string &filename=std::string(), OutputList *outputList = nullptr);
+        /** generates a token list from the given buffer */
+        TokenList(const unsigned char* data, std::size_t size, std::vector<std::string> &filenames, const std::string &filename=std::string(), OutputList *outputList = nullptr);
+        /** generates a token list from the given buffer */
+        TokenList(const char* data, std::size_t size, std::vector<std::string> &filenames, const std::string &filename=std::string(), OutputList *outputList = nullptr);
         /** generates a token list from the given filename parameter */
         TokenList(const std::string &filename, std::vector<std::string> &filenames, OutputList *outputList = nullptr);
         TokenList(const TokenList &other);