diff --git a/include/argparse.hpp b/include/argparse.hpp
index 9a3878c..b14f4b1 100644
--- a/include/argparse.hpp
+++ b/include/argparse.hpp
@@ -964,6 +964,16 @@ namespace argparse
 
                     virtual auto get_name_for_error() const -> std::string = 0;
 
+                    static auto is_negative_number(std::string const & token) -> bool
+                    {
+                        auto num = double();
+                        if (from_string(token, num))
+                        {
+                            return true;
+                        }
+                        return false;
+                    }
+
                 private:
                     ArgumentCommonImpl m_impl;
             };
@@ -1034,10 +1044,7 @@ namespace argparse
                                     {
                                         return true;
                                     }
-                                    auto iss = std::istringstream(token.m_token);
-                                    auto num = double();
-                                    iss >> num;
-                                    if (!iss.fail() && (iss.eof() || iss.peek() == std::istringstream::traits_type::eof()))
+                                    if (is_negative_number(token.m_token))
                                     {
                                         return true;
                                     }
@@ -1412,10 +1419,7 @@ namespace argparse
                                     {
                                         return true;
                                     }
-                                    auto iss = std::istringstream(token.m_token);
-                                    auto num = double();
-                                    iss >> num;
-                                    if (!iss.fail() && (iss.eof() || iss.peek() == std::istringstream::traits_type::eof()))
+                                    if (is_negative_number(token.m_token))
                                     {
                                         return true;
                                     }