diff --git a/modules/PhysiCell_settings.cpp b/modules/PhysiCell_settings.cpp
index a588383d1..be518ce82 100644
--- a/modules/PhysiCell_settings.cpp
+++ b/modules/PhysiCell_settings.cpp
@@ -465,7 +465,7 @@ void Parameter<T>::operator=( T rhs )
 } 
 
 template <class T>
-void Parameter<T>::operator=( Parameter& p )
+void Parameter<T>::operator=( const Parameter& p )
 {
 	name = p.name; 
 	units = p.units; 
diff --git a/modules/PhysiCell_settings.h b/modules/PhysiCell_settings.h
index 86afb2939..0710d3cb4 100644
--- a/modules/PhysiCell_settings.h
+++ b/modules/PhysiCell_settings.h
@@ -174,7 +174,7 @@ class Parameter
 	
 	void operator=( T& rhs ); 
 	void operator=( T rhs ); 
-	void operator=( Parameter& p ); 
+	void operator=( const Parameter& p ); 
 };
 
 template <class T>