diff --git a/include/iapws_r283.h b/include/iapws_r283.h
index c86beba..8242174 100644
--- a/include/iapws_r283.h
+++ b/include/iapws_r283.h
@@ -6,13 +6,19 @@
 #ifndef IAPWS_R283_H
 #define IAPWS_R283_H
 
-extern const double iapws_r283_capi_Tc_H2O; 
-extern const double iapws_r283_capi_Tc_D2O;
+#if _MSC_VER
+#define ADD_IMPORT __declspec(dllimport)
+#else
+#define ADD_IMPORT
+#endif
+
+ADD_IMPORT const double iapws_r283_capi_Tc_H2O; 
+ADD_IMPORT const double iapws_r283_capi_Tc_D2O;
 
-extern const double iapws_r283_capi_pc_H2O;
-extern const double iapws_r283_capi_pc_D2O;
+ADD_IMPORT const double iapws_r283_capi_pc_H2O;
+ADD_IMPORT const double iapws_r283_capi_pc_D2O;
 
-extern const double iapws_r283_capi_rhoc_H2O;
-extern const double iapws_r283_capi_rhoc_D2O;
+ADD_IMPORT const double iapws_r283_capi_rhoc_H2O;
+ADD_IMPORT const double iapws_r283_capi_rhoc_D2O;
 
 #endif