diff --git a/application/argumentparser.h b/application/argumentparser.h
index 1745281..ab38a19 100644
--- a/application/argumentparser.h
+++ b/application/argumentparser.h
@@ -362,7 +362,7 @@ public:
 
 private:
     // declare internal getter/setter/properties/operations for argument definition
-    bool matchesDenotation(const char *denotation, size_t denotationLength) const;
+    bool matchesDenotation(const char *denotation, std::size_t denotationLength) const;
 
     const char *m_name;
     char m_abbreviation;
diff --git a/application/argumentparserprivate.h b/application/argumentparserprivate.h
index 9ec213b..6a24bb7 100644
--- a/application/argumentparserprivate.h
+++ b/application/argumentparserprivate.h
@@ -18,7 +18,7 @@ public:
     /// \brief The Argument instances to store the results. Sub arguments of args are considered as well.
     ArgumentVector &args;
     /// \brief An index which is incremented when an argument is encountered (the current index is stored in the occurrence) or a value is encountered.
-    size_t index;
+    std::size_t index;
     /// \brief Points to the first argument denotation and will be incremented when a denotation has been processed.
     const char *const *argv;
     /// \brief Points to the end of the \a argv array.