diff --git a/trick_source/trick_swig/swig_double.i b/trick_source/trick_swig/swig_double.i
index 81fdc769..1427c866 100644
--- a/trick_source/trick_swig/swig_double.i
+++ b/trick_source/trick_swig/swig_double.i
@@ -1,6 +1,8 @@
 
 %module swig_double
 
+%include "std_string.i"
+
 %{
 
 #include "trick/swig/swig_double.hh"
@@ -11,6 +13,8 @@
 // expose the __str__ function to swig so that it can do pretty prints of parameters with units
 class swig_double {
     public:
+        std::string units;
+
         char * __str__() ;
         char * __repr__() ;
 
diff --git a/trick_source/trick_swig/swig_int.i b/trick_source/trick_swig/swig_int.i
index c2c85bf8..d04bc52a 100644
--- a/trick_source/trick_swig/swig_int.i
+++ b/trick_source/trick_swig/swig_int.i
@@ -1,6 +1,8 @@
 
 %module swig_int
 
+%include "std_string.i"
+
 %{
 
 #include "trick/swig/swig_int.hh"
@@ -11,6 +13,8 @@
 // expose the __str__ function to swig so that it can do pretty prints of parameters with units
 class swig_int {
     public:
+        std::string units;
+
         char * __str__() ;
         char * __repr__() ;