diff --git a/cmdopt.cpp b/cmdopt.cpp
index fded38b4..341161ed 100644
--- a/cmdopt.cpp
+++ b/cmdopt.cpp
@@ -195,7 +195,7 @@ namespace util { namespace cmdopt { namespace option {
 
 ///////////////////////////////////////////////////////////////////////////////
 int
-parser::scan (int argc, char *const *argv)
+parser::scan (int argc, const char *const *argv)
 {
     CHECK_GE (argc, 0);
     CHECK    (argv);
@@ -230,7 +230,7 @@ parser::scan (int argc, char *const *argv)
 
 //-----------------------------------------------------------------------------
 int
-parser::parse_long (int pos, int argc, char *const *argv)
+parser::parse_long (int pos, int argc, const char *const *argv)
 {
     CHECK_LT (pos, argc);
     CHECK_GE (pos, 0);
@@ -276,7 +276,7 @@ parser::parse_long (int pos, int argc, char *const *argv)
 
 //-----------------------------------------------------------------------------
 int
-parser::parse_short (int pos, int argc, char *const *argv)
+parser::parse_short (int pos, int argc, const char *const *argv)
 {
     CHECK_LT (pos, argc);
     CHECK_GE (pos, 0);
diff --git a/cmdopt.hpp b/cmdopt.hpp
index c57651e6..9a77cb09 100644
--- a/cmdopt.hpp
+++ b/cmdopt.hpp
@@ -134,11 +134,11 @@ namespace util { namespace cmdopt {
                 std::string description,
                 Args&&...);
 
-        int scan (int argc, char *const *argv);
+        int scan (int argc, const char *const *argv);
 
     private:
-        int parse_long  (int pos, int argc, char *const *argv);
-        int parse_short (int pos, int argc, char *const *argv);
+        int parse_long  (int pos, int argc, const char *const *argv);
+        int parse_short (int pos, int argc, const char *const *argv);
 
 
         using short_t = std::tuple<char,option::base&>;