diff --git a/Testing/nsconnection_client.m b/Testing/nsconnection_client.m
index bcf4934f4..08f567cd8 100644
--- a/Testing/nsconnection_client.m
+++ b/Testing/nsconnection_client.m
@@ -256,8 +256,14 @@ con_messages (id prx)
 
 #ifdef	_F_BYREF
   [prx sendByref: obj];
-  [prx sendByref:@"hello"];
-  [prx sendByref:[NSDate date]];
+  [prx sendByref: @"hello"];
+  [prx sendByref: [NSDate date]];
+  {
+    NSMutableString	*str = [NSMutableString string];
+
+    [prx modifyByref: str];
+    printf("  Modified '%s'\n", [str lossyCString]);
+  }
 #endif
   printf("  ok\n");
 
diff --git a/Testing/nsconnection_server.m b/Testing/nsconnection_server.m
index 8d8a9d993..794fbdbf0 100644
--- a/Testing/nsconnection_server.m
+++ b/Testing/nsconnection_server.m
@@ -367,6 +367,13 @@
   fflush(stdout);
   return self;
 }
+- modifyByref: (byref NSMutableString *)o
+{
+  printf("  >> byref class is %s\n", object_get_class_name (o));
+  fflush(stdout);
+  [o appendString: @"hello"];
+  return self;
+}
 #endif
 
 - manyArgs: (int)i1 : (int)i2 : (int)i3 : (int)i4 : (int)i5 : (int)i6
diff --git a/Testing/server.h b/Testing/server.h
index fb2260bdf..a44f2f120 100644
--- a/Testing/server.h
+++ b/Testing/server.h
@@ -64,6 +64,7 @@ struct myarray {
 - sendBycopy: (bycopy id)o;
 #ifdef	_F_BYREF
 - sendByref: (byref id)o;
+- modifyByref: (byref NSMutableString *)o;
 #endif
 - manyArgs: (int)i1 : (int)i2 : (int)i3 : (int)i4 : (int)i5 : (int)i6
 : (int)i7 : (int)i8 : (int)i9 : (int)i10 : (int)i11 : (int)i12;