diff --git a/src/max5487/max5487.cxx b/src/max5487/max5487.cxx
index 16b7a78f..44c917c6 100644
--- a/src/max5487/max5487.cxx
+++ b/src/max5487/max5487.cxx
@@ -37,7 +37,7 @@ struct MAX5487Exception : public std::exception {
     const char* what() const throw () { return message.c_str(); }
 };
 
-MAX5487::MAX5487 (int csn = -1) {
+MAX5487::MAX5487 (int csn) {
     mraa_result_t error = MRAA_SUCCESS;
     m_name = "MAX5487";
 
diff --git a/src/max5487/max5487.h b/src/max5487/max5487.h
index c0cca7d9..cf1e8bd6 100644
--- a/src/max5487/max5487.h
+++ b/src/max5487/max5487.h
@@ -62,7 +62,7 @@ class MAX5487 {
          *
          * @param csn to use if any, by default will use ICSP CS (-1)
          */
-        MAX5487 (int csn);
+        MAX5487 (int csn = -1);
 
         /**
          * MAX5487 object destructor, closes all IO connections