diff --git a/Externals/cpp-optparse/OptionParser.h b/Externals/cpp-optparse/OptionParser.h
index aab832c00c25..d9f9ff65ec24 100644
--- a/Externals/cpp-optparse/OptionParser.h
+++ b/Externals/cpp-optparse/OptionParser.h
@@ -77,7 +77,7 @@ class Values {
 class Option {
   public:
     Option(const OptionParser& p) :
-      _parser(p), _action("store"), _type("string"), _nargs(1), _callback(0) {}
+      _parser(p), _action("store"), _type("string"), _nargs(1), _callback(nullptr) {}
     virtual ~Option() {}
 
     Option& action(const std::string& a);
diff --git a/Externals/picojson/picojson.h b/Externals/picojson/picojson.h
index 8d09f05fe163..c136b11c2523 100644
--- a/Externals/picojson/picojson.h
+++ b/Externals/picojson/picojson.h
@@ -1063,7 +1063,7 @@ template <typename Iter> inline std::string parse(value &out, Iter &pos, const I
 
 template <typename Context, typename Iter> inline Iter _parse(Context &ctx, const Iter &first, const Iter &last, std::string *err) {
   input<Iter> in(first, last);
-  if (!_parse(ctx, in) && err != NULL) {
+  if (!_parse(ctx, in) && err != nullptr) {
     char buf[64];
     SNPRINTF(buf, sizeof(buf), "syntax error at line %d near: ", in.line());
     *err = buf;