--- a/src/pt-cmd.h
+++ b/src/pt-cmd.h
@@ -31,7 +31,7 @@
 
 class tree_walker;
 
-#include "pt-base.h"
+#include "pt.h"
 
 // A base class for commands.
 
@@ -46,6 +46,14 @@
   virtual ~tree_command (void) { }
 
   virtual void eval (void) = 0;
+
+private:
+
+  // No copying!
+
+  tree_command (const tree_command&);
+
+  tree_command& operator = (const tree_command&);
 };
 
 // No-op.
@@ -69,6 +77,12 @@
 private:
 
   string orig_cmd;
+
+  // No copying!
+
+  tree_no_op_command (const tree_no_op_command&);
+
+  tree_no_op_command& operator = (const tree_no_op_command&);
 };
 
 #endif