diff --git a/cplusplus/VImage.cpp b/cplusplus/VImage.cpp
index 70d503d3..3143d857 100644
--- a/cplusplus/VImage.cpp
+++ b/cplusplus/VImage.cpp
@@ -169,7 +169,7 @@ VOption::set( const char *name, const char *value )
 
 // input image
 VOption *
-VOption::set( const char *name, const VImage &value )
+VOption::set( const char *name, const VImage value )
 {
 	Pair *pair = new Pair( name );
 
diff --git a/cplusplus/VInterpolate.cpp b/cplusplus/VInterpolate.cpp
index 4d8c326d..cb59715c 100644
--- a/cplusplus/VInterpolate.cpp
+++ b/cplusplus/VInterpolate.cpp
@@ -61,7 +61,7 @@ VInterpolate::new_from_name( const char *name, VOption *options )
 }
 
 VOption *
-VOption::set( const char *name, const VInterpolate &value )
+VOption::set( const char *name, const VInterpolate value )
 {
 	Pair *pair = new Pair( name );
 
diff --git a/cplusplus/VStream.cpp b/cplusplus/VStream.cpp
index 58f4a9d6..ee192a5f 100644
--- a/cplusplus/VStream.cpp
+++ b/cplusplus/VStream.cpp
@@ -111,7 +111,7 @@ VStreamI::new_from_options( const char *options )
 }
 
 VOption *
-VOption::set( const char *name, const VStreamI &value )
+VOption::set( const char *name, const VStreamI value )
 {
 	Pair *pair = new Pair( name );
 
@@ -163,7 +163,7 @@ VStreamO::new_to_memory()
 }
 
 VOption *
-VOption::set( const char *name, const VStreamO &value )
+VOption::set( const char *name, const VStreamO value )
 {
 	Pair *pair = new Pair( name );
 
diff --git a/cplusplus/include/vips/VImage8.h b/cplusplus/include/vips/VImage8.h
index 12b74dfa..e9d85931 100644
--- a/cplusplus/include/vips/VImage8.h
+++ b/cplusplus/include/vips/VImage8.h
@@ -222,10 +222,10 @@ public:
 	VOption *set( const char *name, int value );
 	VOption *set( const char *name, double value );
 	VOption *set( const char *name, const char *value );
-	VOption *set( const char *name, const VImage &value );
-	VOption *set( const char *name, const VInterpolate &value ); 
-	VOption *set( const char *name, const VStreamI &value );
-	VOption *set( const char *name, const VStreamO &value );
+	VOption *set( const char *name, const VImage value );
+	VOption *set( const char *name, const VInterpolate value ); 
+	VOption *set( const char *name, const VStreamI value );
+	VOption *set( const char *name, const VStreamO value );
 	VOption *set( const char *name, std::vector<VImage> value );
 	VOption *set( const char *name, std::vector<double> value );
 	VOption *set( const char *name, std::vector<int> value );