diff --git a/include/CoolPropLib.h b/include/CoolPropLib.h
index cc34fd36..e237fca3 100644
--- a/include/CoolPropLib.h
+++ b/include/CoolPropLib.h
@@ -366,7 +366,7 @@
     * @param buffer_length The length of the buffer for the error code
     * @return
     */
-    EXPORT_CODE void CONVENTION AbstractState_set_binary_interaction_double(const long handle, const size_t i, const size_t j, const char* parameter, const double value, long *errcode, char *message_buffer, const long buffer_length);
+    EXPORT_CODE void CONVENTION AbstractState_set_binary_interaction_double(const long handle, const long i, const long j, const char* parameter, const double value, long *errcode, char *message_buffer, const long buffer_length);
 
     // *************************************************************************************
     // *************************************************************************************
diff --git a/src/CoolPropLib.cpp b/src/CoolPropLib.cpp
index 87397f88..6cda81cc 100644
--- a/src/CoolPropLib.cpp
+++ b/src/CoolPropLib.cpp
@@ -648,7 +648,7 @@ EXPORT_CODE void CONVENTION AbstractState_update_and_5_out(const long handle, co
     }
 }
 
-EXPORT_CODE void CONVENTION AbstractState_set_binary_interaction_double(const long handle, const size_t i, const size_t j, const char* parameter, const double value, long *errcode, char *message_buffer, const long buffer_length)
+EXPORT_CODE void CONVENTION AbstractState_set_binary_interaction_double(const long handle, const long i, const long j, const char* parameter, const double value, long *errcode, char *message_buffer, const long buffer_length)
 {
     *errcode = 0;
     try {