diff --git a/lib/colvars/colvarmodule.cpp b/lib/colvars/colvarmodule.cpp
index a612b87cc6..ee5db06e30 100644
--- a/lib/colvars/colvarmodule.cpp
+++ b/lib/colvars/colvarmodule.cpp
@@ -1552,10 +1552,10 @@ std::string colvarmodule::restart_in_name = "";
 
 
 // i/o constants
-const size_t colvarmodule::it_width = 12;
-const size_t colvarmodule::cv_prec  = 14;
-const size_t colvarmodule::cv_width = 21;
-const size_t colvarmodule::en_prec  = 14;
-const size_t colvarmodule::en_width = 21;
+size_t const colvarmodule::it_width = 12;
+size_t const colvarmodule::cv_prec  = 14;
+size_t const colvarmodule::cv_width = 21;
+size_t const colvarmodule::en_prec  = 14;
+size_t const colvarmodule::en_width = 21;
 const char * const colvarmodule::line_marker = (const char *)
   "----------------------------------------------------------------------\n";