diff --git a/TODO.FACTOR.txt b/TODO.FACTOR.txt
index 04165ca73a..ef3aaf67a9 100644
--- a/TODO.FACTOR.txt
+++ b/TODO.FACTOR.txt
@@ -1,5 +1,7 @@
 + 0.84:
 
+= bug fixes:
+
 - fix contribs: boids, automata
 - sometimes darcs get fails with the httpd
 - gdb triggers 'mutliple i/o ops on port' error
@@ -8,16 +10,18 @@
 - editor:
   - better listener multi-line expression handling
   - history doesn't work in a good way if you ^K the input
-- graphical module manager tool
 - services do not launch if factor not running
 - roundoff is still not quite right with tracks
 - fix top level window positioning
 - nasty inference regressions
 - [ [ dup call ] dup call ] infer hangs
 - the invalid recursion form case needs to be fixed, for inlines too
+
+= features:
+
+- graphical module manager tool
 - instead of decompiling words, add them to a 'recompile' set; compiler
   treats words in the recompile set as if they were not compiled
-- mach_signal: fault address reporting is not reliable
 - see if alien calls can be made faster
 - faster sequence= for UI
 - constant branch folding
@@ -29,6 +33,7 @@
 
 + ui:
 
+- better doc for accumulate, link from tree
 - we have trouble drawing rectangles
 - the UI listener has a shitty design. perhaps it should not call out
   to the real listener.
diff --git a/vm/mach_signal.c b/vm/mach_signal.c
index 13d0da5b94..37d1a47716 100644
--- a/vm/mach_signal.c
+++ b/vm/mach_signal.c
@@ -22,11 +22,11 @@ static mach_port_t our_exception_port;
 /* Communication area for the exception state and thread state.  */
 static SIGSEGV_THREAD_STATE_TYPE save_thread_state;
 
-/* A handler that is called in the faulting thread.  It terminates the thread.  */
+/* A handler that is called in the faulting thread. */
 static void
-terminating_handler ()
+terminating_handler (void *fault_addr)
 {
-  raise (SIGSEGV);
+  memory_protection_error(fault_addr,SIGSEGV);
   abort ();
 }
 
@@ -72,6 +72,7 @@ catch_exception_raise (mach_port_t exception_port,
   save_thread_state = thread_state;
 
   SIGSEGV_PROGRAM_COUNTER (thread_state) = (unsigned long) terminating_handler;
+  pass_arg0(&thread_state,SIGSEGV_EXC_STATE_FAULT(exc_state));
   SIGSEGV_STACK_POINTER (thread_state) = fix_stack_ptr(sp);
 
   /* See http://web.mit.edu/darwin/src/modules/xnu/osfmk/man/thread_set_state.html.  */
diff --git a/vm/os-macosx-ppc.h b/vm/os-macosx-ppc.h
index c3e5556d09..1ec8a2f1f0 100644
--- a/vm/os-macosx-ppc.h
+++ b/vm/os-macosx-ppc.h
@@ -1,13 +1,20 @@
 #define SIGSEGV_EXC_STATE_TYPE ppc_exception_state_t
 #define SIGSEGV_EXC_STATE_FLAVOR PPC_EXCEPTION_STATE
 #define SIGSEGV_EXC_STATE_COUNT PPC_EXCEPTION_STATE_COUNT
+#define SIGSEGV_EXC_STATE_FAULT(exc_state) (exc_state).dar
 #define SIGSEGV_THREAD_STATE_TYPE ppc_thread_state_t
 #define SIGSEGV_THREAD_STATE_FLAVOR PPC_THREAD_STATE
 #define SIGSEGV_THREAD_STATE_COUNT PPC_THREAD_STATE_COUNT
 #define SIGSEGV_STACK_POINTER(thr_state) (thr_state).r1
+#define SIGSEGV_THREAD_STATE_ARG(thr_state) (thr_state).r3
 #define SIGSEGV_PROGRAM_COUNTER(thr_state) (thr_state).srr0
 
 INLINE unsigned long fix_stack_ptr(unsigned long sp)
 {
 	  return sp;
 }
+
+INLINE void pass_arg0(SIGSEGV_THREAD_STATE_TYPE *thr_state, CELL arg)
+{
+	SIGSEGV_THREAD_STATE_ARG(*thr_state) = arg;
+}
diff --git a/vm/os-macosx-x86.h b/vm/os-macosx-x86.h
index 98de91dc4f..0a792a3957 100644
--- a/vm/os-macosx-x86.h
+++ b/vm/os-macosx-x86.h
@@ -1,15 +1,23 @@
 #define SIGSEGV_EXC_STATE_TYPE i386_exception_state_t
 #define SIGSEGV_EXC_STATE_FLAVOR i386_EXCEPTION_STATE
 #define SIGSEGV_EXC_STATE_COUNT i386_EXCEPTION_STATE_COUNT
+#define SIGSEGV_EXC_STATE_FAULT(exc_state) (exc_state).dar
 #define SIGSEGV_THREAD_STATE_TYPE i386_thread_state_t
 #define SIGSEGV_THREAD_STATE_FLAVOR i386_THREAD_STATE
 #define SIGSEGV_THREAD_STATE_COUNT i386_THREAD_STATE_COUNT
 #define SIGSEGV_STACK_POINTER(thr_state) (thr_state).esp
 #define SIGSEGV_PROGRAM_COUNTER(thr_state) (thr_state).eip
 
+/* Adjust stack pointer so we can push an arg */
 INLINE unsigned long fix_stack_ptr(unsigned long sp)
 {
 	  if ((sp & 0xf) != 0) sp -= (sp & 0xf);
-	  sp -= 4;
+	  sp -= 8;
 	  return sp;
 }
+
+INLINE void pass_arg0(SIGSEGV_THREAD_STATE_TYPE *thr_state, CELL arg)
+{
+	*SIGSEGV_STACK_POINTER(*thread_state) = arg;
+	SIGSEGV_STACK_POINTER(*thread_state) -= CELLS;
+}