diff --git a/Source/sources/Castro_sources.H b/Source/sources/Castro_sources.H
index 16eeb3a17e..c40958d99f 100644
--- a/Source/sources/Castro_sources.H
+++ b/Source/sources/Castro_sources.H
@@ -149,7 +149,7 @@
 ///
 /// @param update       Real Vector of changes
 ///
-    static void print_source_change(amrex::Vector<amrex::Real> update);
+    static void print_source_change(const amrex::Vector<amrex::Real>& update);
 
 
 ///
diff --git a/Source/sources/Castro_sources.cpp b/Source/sources/Castro_sources.cpp
index cae99300a7..7341946150 100644
--- a/Source/sources/Castro_sources.cpp
+++ b/Source/sources/Castro_sources.cpp
@@ -459,7 +459,7 @@ Castro::evaluate_source_change(const MultiFab& source, Real dt, bool local)
 // interested in printing changes to energy, mass, etc.
 
 void
-Castro::print_source_change(Vector<Real> update)
+Castro::print_source_change(const Vector<Real>& update)
 {
 
   if (ParallelDescriptor::IOProcessor()) {