Index: src/Common/GC.cc
===================================================================
--- src/Common/GC.cc	(revision 8d7bef249652cc2b9854c7090c758bcd9ad9f613)
+++ src/Common/GC.cc	(revision 7e4b44db4aee3e4db9e5c3f78521d2db85fd048b)
@@ -17,4 +17,5 @@
 
 #include <algorithm>
+#include <cassert>
 
 GC& GC::get() {
@@ -101,6 +102,14 @@
 }
 
+bool stack_check( int* i, GC_Object* o ) {
+	int j;
+	return ( i < &j ) == ( (void*)o < (void*)&j );
+}
+
 GC_Object::GC_Object() {
 	GC::get().register_object( this );
+
+	int i;
+	assert(!stack_check(&i, this));
 }
 
Index: src/Common/PassVisitor.h
===================================================================
--- src/Common/PassVisitor.h	(revision 8d7bef249652cc2b9854c7090c758bcd9ad9f613)
+++ src/Common/PassVisitor.h	(revision 7e4b44db4aee3e4db9e5c3f78521d2db85fd048b)
@@ -148,5 +148,5 @@
 	virtual void visit( Subrange * subrange ) override final;
 
-	virtual void visit( Constant * constant ) override final;
+	virtual void visit( Constant * constant ) final;
 
 	virtual void visit( Attribute * attribute ) override final;
@@ -245,5 +245,5 @@
 	virtual Subrange * mutate( Subrange * subrange ) override final;
 
-	virtual Constant * mutate( Constant * constant ) override final;
+	virtual Constant * mutate( Constant * constant ) final;
 
 	virtual Attribute * mutate( Attribute * attribute ) override final;
Index: src/SynTree/Constant.h
===================================================================
--- src/SynTree/Constant.h	(revision 8d7bef249652cc2b9854c7090c758bcd9ad9f613)
+++ src/SynTree/Constant.h	(revision 7e4b44db4aee3e4db9e5c3f78521d2db85fd048b)
@@ -19,11 +19,12 @@
 #include <string>     // for string
 
-#include "BaseSyntaxNode.h"
 #include "Mutator.h"  // for Mutator
 #include "Visitor.h"  // for Visitor
 
+#include "Common/Indenter.h"  // for Indenter
+
 class Type;
 
-class Constant : public BaseSyntaxNode {
+class Constant {
   public:
 	Constant( Type * type, std::string rep, unsigned long long val );