diff --git a/lily/accidental-engraver.cc b/lily/accidental-engraver.cc
index 39a66ba..20f0103 100644
--- a/lily/accidental-engraver.cc
+++ b/lily/accidental-engraver.cc
@@ -402,7 +402,7 @@ Accidental_engraver::make_standard_accid
     = make_grob_from_properties (trans,
 				 ly_symbol2scm ("Accidental"),
 				 note_head->self_scm (),
-				 "Accidental");
+				 "Accidental", __FILE__, __LINE__);
 
   /*
     We add the accidentals to the support of the arpeggio,
@@ -442,7 +442,7 @@ Accidental_engraver::make_suggested_acci
     = make_grob_from_properties (trans,
 				 ly_symbol2scm ("AccidentalSuggestion"),
 				 note_head->self_scm (),
-				 "AccidentalSuggestion");
+				 "AccidentalSuggestion", __FILE__, __LINE__);
 
   Side_position_interface::add_support (a, note_head);
   if (Grob *stem = unsmob_grob (a->get_object ("stem")))
diff --git a/lily/align-interface.cc b/lily/align-interface.cc
index afe4702..b2160d0 100644
--- a/lily/align-interface.cc
+++ b/lily/align-interface.cc
@@ -323,7 +323,7 @@ Align_interface::add_element (Grob *me, 
   SCM sym = axis_offset_symbol (a);
   SCM proc = axis_parent_positioning (a);
     
-  element->internal_set_property (sym, proc);
+  element->internal_set_property (sym, proc, __FILE__, __LINE__);
   Axis_group_interface::add_element (me, element);
 }
 
diff --git a/lily/axis-group-interface.cc b/lily/axis-group-interface.cc
index 1d509f0..2727751 100644
--- a/lily/axis-group-interface.cc
+++ b/lily/axis-group-interface.cc
@@ -37,7 +37,7 @@ Axis_group_interface::add_element (Grob 
       e->internal_set_object ((a == X_AXIS)
 			      ? ly_symbol2scm ("axis-group-parent-X")
 			      : ly_symbol2scm ("axis-group-parent-Y"),
-			      me->self_scm ());
+			      me->self_scm (), __FILE__, __LINE__);
     }
 
   /* must be ordered, because Align_interface also uses
diff --git a/lily/break-align-engraver.cc b/lily/break-align-engraver.cc
index e6a7935..7b4f4b7 100644
--- a/lily/break-align-engraver.cc
+++ b/lily/break-align-engraver.cc
@@ -85,7 +85,7 @@ Break_align_engraver::acknowledge_break_
 	  left_edge_ = make_item_from_properties (random_source,
 						  ly_symbol2scm ("LeftEdge"),
 						  SCM_EOL,
-						  "LeftEdge");
+						  "LeftEdge", __FILE__, __LINE__);
 	  add_to_group (left_edge_->get_property ("break-align-symbol"),
 			left_edge_);
 	}
diff --git a/lily/break-substitution.cc b/lily/break-substitution.cc
index 0c1e996..8d65f6b 100644
--- a/lily/break-substitution.cc
+++ b/lily/break-substitution.cc
@@ -397,7 +397,7 @@ Spanner::fast_substitute_grob_array (SCM
       if (!unsmob_grob_array (newval))
 	{
 	  newval = Grob_array::make_array ();
-	  sc->internal_set_object (sym, newval);
+	  sc->internal_set_object (sym, newval, __FILE__, __LINE__);
 	}
 
       Grob_array *new_array = unsmob_grob_array (newval);
@@ -500,14 +500,14 @@ Spanner::substitute_one_mutable_property
 	    if (!unsmob_grob_array (newval))
 	      {
 		newval = Grob_array::make_array ();
-		sc->internal_set_object (sym, newval);
+		sc->internal_set_object (sym, newval, __FILE__, __LINE__);
 	      }
 	    substitute_grob_array (grob_array, unsmob_grob_array (newval));
 	  }
 	else
 	  {
 	    SCM newval = do_break_substitution (val);
-	    sc->internal_set_object (sym, newval);
+	    sc->internal_set_object (sym, newval, __FILE__, __LINE__);
 	  }
       }
 }
diff --git a/lily/context-property.cc b/lily/context-property.cc
index 502fc92..0f77cfd 100644
--- a/lily/context-property.cc
+++ b/lily/context-property.cc
@@ -118,7 +118,7 @@ execute_general_pushpop_property (Contex
 	{
 	  SCM base = updated_grob_properties (context, context_property);
 	  current_context_val = scm_cons (base, base);
-	  context->internal_set_property (context_property, current_context_val);
+	  context->internal_set_property (context_property, current_context_val, __FILE__, __LINE__);
 	}
 
       if (!scm_is_pair (current_context_val))
@@ -180,7 +180,7 @@ execute_general_pushpop_property (Contex
       if (new_alist == daddy)
 	context->unset_property (context_property);
       else
-	context->internal_set_property (context_property, scm_cons (new_alist, daddy));
+	context->internal_set_property (context_property, scm_cons (new_alist, daddy), __FILE__, __LINE__);
     }
 }
 
@@ -224,7 +224,7 @@ apply_property_operations (Context *tg, 
 	  execute_general_pushpop_property (tg, context_prop, grob_prop_path, val);
 	}
       else if (type == ly_symbol2scm ("assign"))
-	tg->internal_set_property (scm_car (entry), scm_cadr (entry));
+	tg->internal_set_property (scm_car (entry), scm_cadr (entry), __FILE__, __LINE__);
     }
 }
 
@@ -275,8 +275,23 @@ updated_grob_properties (Context *tg, SC
     }
 }
 
+static SCM creation_callback = SCM_EOL;
+LY_DEFINE (ly_set_grob_creation_callback, "ly:set-grob-creation-callback",
+	   1, 0, 0, (SCM cb),
+	   "Specify a procedure that will be called every time a new grob "
+	   "is created. The callback will receive as arguments the grob "
+	   "that was created, the name of the C++ source file that caused "
+	   "the grob to be created and the corresponding line number in the "
+	   "C++ source file.")
+{
+  if (!ly_is_procedure (cb))
+    warning (_ ("not setting creation callback: not a procedure"));
+  else
+    creation_callback = cb;
+}
+
 Grob *
-make_grob_from_properties (Engraver *tr, SCM symbol, SCM cause, char const *name)
+make_grob_from_properties (Engraver *tr, SCM symbol, SCM cause, char const *name, char const *file, int line)
 {
   Context *context = tr->context ();
 
@@ -298,27 +313,31 @@ make_grob_from_properties (Engraver *tr,
   assert (grob);
   dynamic_cast<Engraver *> (tr)->announce_grob (grob, cause);
 
+  if (ly_is_procedure (creation_callback))
+    scm_apply_0 (creation_callback,
+		 scm_list_n (grob->self_scm (), scm_makfrom0str (file), scm_from_int (line), SCM_UNDEFINED));
+
   return grob;
 }
 
 Item *
-make_item_from_properties (Engraver *tr, SCM x, SCM cause, char const *name)
+make_item_from_properties (Engraver *tr, SCM x, SCM cause, char const *name, char const *file, int line)
 {
-  Item *it = dynamic_cast<Item *> (make_grob_from_properties (tr, x, cause, name));
+  Item *it = dynamic_cast<Item *> (make_grob_from_properties (tr, x, cause, name, file, line));
   assert (it);
   return it;
 }
 
 Paper_column *
-make_paper_column_from_properties (Engraver *tr, SCM x, char const *name)
+make_paper_column_from_properties (Engraver *tr, SCM x, char const *name, char const *file, int line)
 {
-  return dynamic_cast<Paper_column *> (make_grob_from_properties (tr, x, SCM_EOL, name));
+  return dynamic_cast<Paper_column *> (make_grob_from_properties (tr, x, SCM_EOL, name, file, line));
 }
 
 Spanner *
-make_spanner_from_properties (Engraver *tr, SCM x, SCM cause, char const *name)
+make_spanner_from_properties (Engraver *tr, SCM x, SCM cause, char const *name, char const *file, int line)
 {
-  Spanner *sp = dynamic_cast<Spanner *> (make_grob_from_properties (tr, x, cause, name));
+  Spanner *sp = dynamic_cast<Spanner *> (make_grob_from_properties (tr, x, cause, name, file, line));
   assert (sp);
   return sp;
 }
diff --git a/lily/context-scheme.cc b/lily/context-scheme.cc
index 92240a9..1a28a1e 100644
--- a/lily/context-scheme.cc
+++ b/lily/context-scheme.cc
@@ -84,7 +84,7 @@ LY_DEFINE (ly_context_set_property, "ly:
   SCM_ASSERT_TYPE (tr, context, SCM_ARG1, __FUNCTION__, "Context");
   SCM_ASSERT_TYPE (scm_is_symbol (name), name, SCM_ARG2, __FUNCTION__, "symbol");
 
-  tr->internal_set_property (name, val);
+  tr->internal_set_property (name, val, __FILE__, __LINE__);
 
   return SCM_UNSPECIFIED;
 }
diff --git a/lily/context.cc b/lily/context.cc
index 5211cbb..e625509 100644
--- a/lily/context.cc
+++ b/lily/context.cc
@@ -238,7 +238,7 @@ Context::set_property_from_event (SCM se
       if (val != SCM_EOL)
 	ok = type_check_assignment (sym, val, ly_symbol2scm ("translation-type?"));
       if (ok)
-	internal_set_property (sym, val);
+	internal_set_property (sym, val, __FILE__, __LINE__);
     }
 }
 
@@ -444,7 +444,7 @@ Context::internal_send_stream_event (SCM
   Stream_event *e = new Stream_event (type, origin);
   for (int i = 0; props[i]; i += 2)
     {
-      e->internal_set_property (props[i], props[i+1]);
+      e->internal_set_property (props[i], props[i+1], __FILE__, __LINE__);
     }
   event_source_->broadcast (e);
   e->unprotect ();
@@ -469,7 +469,7 @@ Context::add_alias (SCM sym)
 }
 
 void
-Context::internal_set_property (SCM sym, SCM val)
+Context::internal_set_property (SCM sym, SCM val, char const *file, int line)
 {
 #ifndef NDEBUG
   if (do_internal_type_checking_global)
@@ -737,7 +737,7 @@ measure_position (Context const *context
 void
 set_context_property_on_children (Context *trans, SCM sym, SCM val)
 {
-  trans->internal_set_property (sym, ly_deep_copy (val));
+  trans->internal_set_property (sym, ly_deep_copy (val), __FILE__, __LINE__);
   for (SCM p = trans->children_contexts (); scm_is_pair (p); p = scm_cdr (p))
     {
       Context *trg = unsmob_context (scm_car (p));
diff --git a/lily/grob-closure.cc b/lily/grob-closure.cc
index 81bd393..e258f81 100644
--- a/lily/grob-closure.cc
+++ b/lily/grob-closure.cc
@@ -38,7 +38,7 @@ add_offset_callback (Grob *g, SCM proc, 
       && !is_simple_closure (data))
     {
       g->internal_set_property (axis_offset_symbol (a),
-				proc);
+				proc, __FILE__, __LINE__);
       return ;
     }
 
@@ -54,7 +54,7 @@ add_offset_callback (Grob *g, SCM proc, 
   
   SCM expr = scm_list_3 (plus, proc, data);
   g->internal_set_property (axis_offset_symbol (a),
-			    ly_make_simple_closure (expr));
+			    ly_make_simple_closure (expr), __FILE__, __LINE__);
 }
 
 
@@ -85,5 +85,6 @@ chain_offset_callback (Grob *g, SCM proc
 			    
 			    // twice: one as a wrapper for grob property routines,
 			    // once for the actual delayed binding. 
-			    ly_make_simple_closure (ly_make_simple_closure (expr)));
+			    ly_make_simple_closure (ly_make_simple_closure (expr)),
+			    __FILE__, __LINE__);
 }
diff --git a/lily/grob-property.cc b/lily/grob-property.cc
index 8d7ecc0..7d090d2 100644
--- a/lily/grob-property.cc
+++ b/lily/grob-property.cc
@@ -11,12 +11,32 @@ #include "misc.hh"
 #include "paper-score.hh"
 #include "output-def.hh"
 #include "spanner.hh"
+#include "international.hh"
 #include "item.hh"
 #include "misc.hh"
 #include "item.hh"
 #include "program-option.hh"
 #include "profile.hh"
 #include "simple-closure.hh"
+#include "warn.hh"
+
+static SCM modification_callback = SCM_EOL;
+
+LY_DEFINE (ly_set_grob_modification_callback, "ly:set-grob-modification-callback",
+	   1, 0, 0, (SCM cb),
+	   "Specify a procedure that will be called every time lilypond modifies "
+	   "a grob property. The callback will receive as arguments "
+	   "the grob that is being modified, the name of the C++ file in which "
+	   "the modification was requested, the line number in the C++ file in "
+	   "which the modification was requested, the property to be changed and "
+	   "the new value for the property.")
+{
+  if (!ly_is_procedure (cb))
+    warning (_ ("not setting modification callback: not a procedure"));
+  else
+    modification_callback = cb;
+  return SCM_EOL;
+}
 
 SCM
 Grob::get_property_alist_chain (SCM def) const
@@ -31,7 +51,7 @@ Grob::get_property_alist_chain (SCM def)
 extern void check_interfaces_for_property (Grob const *me, SCM sym);
 
 void
-Grob::internal_set_property (SCM sym, SCM v)
+Grob::internal_set_property (SCM sym, SCM v, char const *file, int line)
 {
 #ifndef NDEBUG
   SCM grob_p = ly_lily_module_constant ("ly:grob?");
@@ -60,6 +80,12 @@ #endif
 	abort ();
       check_interfaces_for_property (this, sym);
     }
+  protect ();
+  if (ly_is_procedure (modification_callback))
+      scm_apply_0 (modification_callback,
+		   scm_list_n (self_scm (), scm_makfrom0str (file), scm_from_int (line),
+			       sym, v, SCM_UNDEFINED));
+  unprotect ();
 
   mutable_property_alist_ = scm_assq_set_x (mutable_property_alist_, sym, v);
 }
@@ -155,23 +181,28 @@ #endif
 	mutable_property_alist_ = scm_assq_remove_x (mutable_property_alist_, marker);
     }
   else
-    internal_set_property (sym, value);
+    internal_set_property (sym, value, __FILE__, __LINE__);
 	  
   return value;
 }
 
 void
-Grob::internal_set_object (SCM s, SCM v)
+Grob::internal_set_object (SCM s, SCM v, char const *file, int line)
 {
   /* Perhaps we simply do the assq_set, but what the heck. */
   if (!is_live ())
     return;
 
+  if (ly_is_procedure (modification_callback))
+    scm_apply_0 (modification_callback,
+		 scm_list_n (self_scm (), scm_makfrom0str (file), scm_from_int (line),
+			     s, v, SCM_UNDEFINED));
+
   object_alist_ = scm_assq_set_x (object_alist_, s, v);
 }
 
 void
-Grob::del_property (SCM sym)
+Grob::internal_del_property (SCM sym, char const *file, int line)
 {
   mutable_property_alist_ = scm_assq_remove_x (mutable_property_alist_, sym);
 }
diff --git a/lily/grob-scheme.cc b/lily/grob-scheme.cc
index bca86f5..3245d33 100644
--- a/lily/grob-scheme.cc
+++ b/lily/grob-scheme.cc
@@ -42,7 +42,7 @@ LY_DEFINE (ly_grob_set_property_x, "ly:g
       && !type_check_assignment (sym, val, ly_symbol2scm ("backend-type?")))
     error ("typecheck failed");
 
-  sc->internal_set_property (sym, val);
+  sc->internal_set_property (sym, val, __FILE__, __LINE__);
   return SCM_UNSPECIFIED;
 }
 
diff --git a/lily/grob.cc b/lily/grob.cc
index 72b4637..fdbb2c8 100644
--- a/lily/grob.cc
+++ b/lily/grob.cc
@@ -336,7 +336,7 @@ Grob::get_offset (Axis a) const
   if (me->dim_cache_[a].offset_)
     {
       *me->dim_cache_[a].offset_ += off;
-      me->del_property (sym);
+      me->del_property ((a == X_AXIS) ? "X-offset" : "Y-offset");
       return *me->dim_cache_[a].offset_;
     }
   else
@@ -365,7 +365,7 @@ Grob::flush_extent_cache (Axis axis)
 	Ugh, this is not accurate; will flush property, causing
 	callback to be called if.
        */
-      del_property ((axis == X_AXIS) ? ly_symbol2scm ("X-extent") : ly_symbol2scm ("Y-extent"));
+      del_property ((axis == X_AXIS) ? "X-extent" : "Y-extent");
       delete dim_cache_[axis].extent_;
       dim_cache_[axis].extent_ = 0;
       if (get_parent (axis))
diff --git a/lily/include/context.hh b/lily/include/context.hh
index 1a9c0c2..334aabe 100644
--- a/lily/include/context.hh
+++ b/lily/include/context.hh
@@ -87,7 +87,7 @@ public:
   /* properties:  */
   SCM internal_get_property (SCM name_sym) const;
   SCM properties_as_alist () const;
-  void internal_set_property (SCM var_sym, SCM value);
+  void internal_set_property (SCM var_sym, SCM value, char const *file, int line);
   Context *where_defined (SCM name_sym, SCM *value) const;
   void unset_property (SCM var_sym);
 
diff --git a/lily/include/engraver.hh b/lily/include/engraver.hh
index 04a7623..2c407d4 100644
--- a/lily/include/engraver.hh
+++ b/lily/include/engraver.hh
@@ -46,12 +46,12 @@ public:
   TRANSLATOR_DECLARATIONS (Engraver);
 };
 
-#define make_item(x, cause) make_item_from_properties (this, ly_symbol2scm (x), cause, x)
-#define make_spanner(x, cause) make_spanner_from_properties (this, ly_symbol2scm (x), cause, x)
-#define make_paper_column(x) make_paper_column_from_properties (this, ly_symbol2scm (x), x)
-Grob *make_grob_from_properties (Engraver *tr, SCM symbol, SCM cause, char const *name);
-Item *make_item_from_properties (Engraver *tg, SCM x, SCM cause, char const *name);
-Spanner *make_spanner_from_properties (Engraver *tg, SCM x, SCM cause, char const *name);
-Paper_column *make_paper_column_from_properties (Engraver *tg, SCM x, char const *name);
+#define make_item(x, cause) make_item_from_properties (this, ly_symbol2scm (x), cause, x, __FILE__, __LINE__)
+#define make_spanner(x, cause) make_spanner_from_properties (this, ly_symbol2scm (x), cause, x, __FILE__, __LINE__)
+#define make_paper_column(x) make_paper_column_from_properties (this, ly_symbol2scm (x), x, __FILE__, __LINE__)
+Grob *make_grob_from_properties (Engraver *tr, SCM symbol, SCM cause, char const *name, char const *file, int line);
+Item *make_item_from_properties (Engraver *tg, SCM x, SCM cause, char const *name, char const *file, int line);
+Spanner *make_spanner_from_properties (Engraver *tg, SCM x, SCM cause, char const *name, char const *file, int line);
+Paper_column *make_paper_column_from_properties (Engraver *tg, SCM x, char const *name, char const *file, int line);
 
 #endif // ENGRAVER_HH
diff --git a/lily/include/grob.hh b/lily/include/grob.hh
index e2bc015..a4184ac 100644
--- a/lily/include/grob.hh
+++ b/lily/include/grob.hh
@@ -80,9 +80,9 @@ public:
   SCM internal_get_property (SCM symbol) const;
   SCM get_property_data (SCM symbol) const;
   SCM internal_get_object (SCM symbol) const;
-  void del_property (SCM symbol); 
-  void internal_set_property (SCM sym, SCM val);
-  void internal_set_object (SCM sym, SCM val);
+  void internal_del_property (SCM symbol, char const *file, int line); 
+  void internal_set_property (SCM sym, SCM val, char const *file, int line);
+  void internal_set_object (SCM sym, SCM val, char const *file, int line);
 
   /* messages */  
   void warning (string) const;
@@ -146,5 +146,4 @@ void chain_offset_callback (Grob *g, SCM
 SCM axis_offset_symbol (Axis a);
 SCM axis_parent_positioning (Axis a);
 
-
 #endif /* GROB_HH */
diff --git a/lily/include/lily-guile-macros.hh b/lily/include/lily-guile-macros.hh
index ef0db47..7002c0f 100644
--- a/lily/include/lily-guile-macros.hh
+++ b/lily/include/lily-guile-macros.hh
@@ -150,7 +150,8 @@ #define LY_DEFINE_MEMBER_FUNCTION(CLASS,
 
 #define get_property(x) internal_get_property (ly_symbol2scm (x))
 #define get_object(x) internal_get_object (ly_symbol2scm (x))
-#define set_property(x, y) internal_set_property (ly_symbol2scm (x), y)
-#define set_object(x, y) internal_set_object (ly_symbol2scm (x), y)
+#define del_property(x) internal_del_property (ly_symbol2scm (x), __FILE__, __LINE__)
+#define set_property(x, y) internal_set_property (ly_symbol2scm (x), y, __FILE__, __LINE__)
+#define set_object(x, y) internal_set_object (ly_symbol2scm (x), y, __FILE__, __LINE__)
 
 #endif /* LILY_GUILE_MACROS_HH */
diff --git a/lily/include/prob.hh b/lily/include/prob.hh
index 141aba4..04ef769 100644
--- a/lily/include/prob.hh
+++ b/lily/include/prob.hh
@@ -40,7 +40,7 @@ public:
   SCM type () const { return type_; }
   SCM get_property_alist (bool mutble) const;
   SCM internal_get_property (SCM sym) const;
-  void internal_set_property (SCM sym, SCM val);
+  void internal_set_property (SCM sym, SCM val, const char *file, int line);
 };
 DECLARE_UNSMOB(Prob,prob);
 SCM ly_prob_set_property_x (SCM system, SCM sym, SCM value);
diff --git a/lily/parenthesis-engraver.cc b/lily/parenthesis-engraver.cc
index 01ea191..d8bda5d 100644
--- a/lily/parenthesis-engraver.cc
+++ b/lily/parenthesis-engraver.cc
@@ -43,7 +43,7 @@ Parenthesis_engraver::acknowledge_grob (
 	      Item *paren = make_item_from_properties (eng,
 						       ly_symbol2scm ("ParenthesesItem"),
 						       victim->self_scm (),
-						       "ParenthesesItem");
+						       "ParenthesesItem", __FILE__, __LINE__);
 
 	      Pointer_group_interface::add_grob (paren, ly_symbol2scm ("elements"), victim);
 	      
diff --git a/lily/parser.yy b/lily/parser.yy
index ef215c3..defa3b9 100644
--- a/lily/parser.yy
+++ b/lily/parser.yy
@@ -2491,7 +2491,7 @@ void
 set_music_properties (Music *p, SCM a)
 {
   for (SCM k = a; scm_is_pair (k); k = scm_cdr (k))
- 	p->internal_set_property (scm_caar (k), scm_cdar (k));
+ 	p->internal_set_property (scm_caar (k), scm_cdar (k), __FILE__, __LINE__);
 }
 
 
diff --git a/lily/pointer-group-interface.cc b/lily/pointer-group-interface.cc
index 1ab1d02..508f9ea 100644
--- a/lily/pointer-group-interface.cc
+++ b/lily/pointer-group-interface.cc
@@ -42,7 +42,7 @@ Pointer_group_interface::get_grob_array 
     {
       scm_arr = Grob_array::make_array ();
       arr = unsmob_grob_array (scm_arr);
-      me->internal_set_object (sym, scm_arr);
+      me->internal_set_object (sym, scm_arr, __FILE__, __LINE__);
     }
   return arr;
 }
diff --git a/lily/prob-scheme.cc b/lily/prob-scheme.cc
index ceadabd..2d473b3 100644
--- a/lily/prob-scheme.cc
+++ b/lily/prob-scheme.cc
@@ -16,7 +16,7 @@ LY_DEFINE (ly_prob_set_property_x, "ly:p
   SCM_ASSERT_TYPE (ps, obj, SCM_ARG1, __FUNCTION__, "Prob");
   SCM_ASSERT_TYPE (scm_is_symbol (sym), sym, SCM_ARG2, __FUNCTION__, "symbol");
 
-  ps->internal_set_property (sym, value);
+  ps->internal_set_property (sym, value, __FILE__, __LINE__);
   return SCM_UNSPECIFIED;
 }
 
@@ -70,7 +70,7 @@ LY_DEFINE (ly_make_prob, "ly:make-prob",
       SCM sym = scm_car (s);
       SCM val = scm_cadr (s);
 
-      pr->internal_set_property (sym, val);
+      pr->internal_set_property (sym, val, __FILE__, __LINE__);
     }
   
   return pr->unprotect ();
diff --git a/lily/prob.cc b/lily/prob.cc
index 2640bdf..de80894 100644
--- a/lily/prob.cc
+++ b/lily/prob.cc
@@ -99,7 +99,7 @@ Prob::internal_get_property (SCM sym) co
 }
 
 void
-Prob::internal_set_property (SCM sym, SCM val) 
+Prob::internal_set_property (SCM sym, SCM val, char const *file, int line) 
 {
   if (do_internal_type_checking_global)
     type_check_assignment (sym, val);
diff --git a/lily/script-engraver.cc b/lily/script-engraver.cc
index 7c05131..9c67037 100644
--- a/lily/script-engraver.cc
+++ b/lily/script-engraver.cc
@@ -84,7 +84,7 @@ copy_property (Grob *g, SCM sym, SCM ali
     {
       SCM entry = scm_assoc (sym, alist);
       if (scm_is_pair (entry))
-	g->internal_set_property (sym, scm_cdr (entry));
+	g->internal_set_property (sym, scm_cdr (entry), __FILE__, __LINE__);
     }
 }
 
@@ -135,7 +135,7 @@ void make_script_from_event (Grob *p,  C
       SCM preset = p->get_property_data (sym);
       if (val == SCM_EOL
 	  || scm_call_1 (type, preset) == SCM_BOOL_F)
-	p->internal_set_property (sym, val);
+	p->internal_set_property (sym, val, __FILE__, __LINE__);
     }
 
   if (!priority_found)
diff --git a/lily/span-bar-engraver.cc b/lily/span-bar-engraver.cc
index 503bdf2..6d4bbb4 100644
--- a/lily/span-bar-engraver.cc
+++ b/lily/span-bar-engraver.cc
@@ -65,7 +65,7 @@ Span_bar_engraver::stop_translation_time
       SCM vissym = ly_symbol2scm ("break-visibility");
       SCM vis = bars_[0]->internal_get_property (vissym);
       if (ly_is_equal (spanbar_->internal_get_property (vissym), vis))
-	spanbar_->internal_set_property (vissym, vis);
+	spanbar_->internal_set_property (vissym, vis, __FILE__, __LINE__);
 
       spanbar_ = 0;
     }
diff --git a/lily/system-start-delimiter-engraver.cc b/lily/system-start-delimiter-engraver.cc
index b03c1d2..9de8039 100644
--- a/lily/system-start-delimiter-engraver.cc
+++ b/lily/system-start-delimiter-engraver.cc
@@ -77,7 +77,7 @@ Bracket_nesting_group::create_grobs (Eng
 {
   SCM type = scm_is_symbol (symbol_) ? symbol_ : default_type;
   delimiter_ = make_spanner_from_properties (engraver, type,
-					     SCM_EOL, ly_symbol2string (type).c_str ());
+					     SCM_EOL, ly_symbol2string (type).c_str (), __FILE__, __LINE__);
 
   for (vsize i = 0 ; i < children_.size (); i++)
     {
diff --git a/lily/tuplet-bracket.cc b/lily/tuplet-bracket.cc
index fa5d9a9..b81107c 100644
--- a/lily/tuplet-bracket.cc
+++ b/lily/tuplet-bracket.cc
@@ -70,7 +70,7 @@ flatten_number_pair_property (Grob *me,
     = robust_scm2drul (me->internal_get_property (sym), zero);
   pair[xdir] = 0.0;
   
-  me->internal_set_property (sym, ly_interval2scm (pair));
+  me->internal_set_property (sym, ly_interval2scm (pair), __FILE__, __LINE__);
 }
 
 
diff --git a/lily/tweak-engraver.cc b/lily/tweak-engraver.cc
index 9843dce..a479935 100644
--- a/lily/tweak-engraver.cc
+++ b/lily/tweak-engraver.cc
@@ -33,7 +33,7 @@ Tweak_engraver::acknowledge_grob (Grob_i
       for (SCM s = music->get_property ("tweaks");
 	   scm_is_pair (s); s = scm_cdr (s))
 	{
-	  info.grob ()->internal_set_property (scm_caar (s), scm_cdar (s));
+	  info.grob ()->internal_set_property (scm_caar (s), scm_cdar (s), __FILE__, __LINE__);
 	}
     }
 }
diff --git a/lily/volta-repeat-iterator.cc b/lily/volta-repeat-iterator.cc
index 31f6295..a94101a 100644
--- a/lily/volta-repeat-iterator.cc
+++ b/lily/volta-repeat-iterator.cc
@@ -69,7 +69,7 @@ Volta_repeat_iterator::add_repeat_comman
       && current_reps == SCM_EOL || scm_is_pair (current_reps))
     {
       current_reps = scm_cons (what, current_reps);
-      where->internal_set_property (reps, current_reps);
+      where->internal_set_property (reps, current_reps, __FILE__, __LINE__);
     }
 }