diff --git a/vm/callstack.c b/vm/callstack.c
index 5c3ab0ea79..4461d39b1c 100644
--- a/vm/callstack.c
+++ b/vm/callstack.c
@@ -40,6 +40,16 @@ F_CALLSTACK *allot_callstack(CELL size)
 	return callstack;
 }
 
+F_STACK_FRAME *fix_callstack_top(F_STACK_FRAME *top, F_STACK_FRAME *bottom)
+{
+	F_STACK_FRAME *frame = bottom - 1;
+
+	while(frame >= top)
+		frame = frame_successor(frame);
+
+	return frame + 1;
+}
+
 /* We ignore the topmost frame, the one calling 'callstack',
 so that set-callstack doesn't get stuck in an infinite loop.
 
diff --git a/vm/callstack.h b/vm/callstack.h
index 564dea9738..4033820184 100644
--- a/vm/callstack.h
+++ b/vm/callstack.h
@@ -5,6 +5,7 @@ F_FASTCALL __attribute__((noinline)) void save_callstack_top(F_STACK_FRAME *call
 
 typedef void (*CALLSTACK_ITER)(F_STACK_FRAME *frame);
 
+F_STACK_FRAME *fix_callstack_top(F_STACK_FRAME *top, F_STACK_FRAME *bottom);
 void iterate_callstack(CELL top, CELL bottom, CALLSTACK_ITER iterator);
 void iterate_callstack_object(F_CALLSTACK *stack, CALLSTACK_ITER iterator);
 F_STACK_FRAME *frame_successor(F_STACK_FRAME *frame);
diff --git a/vm/errors.c b/vm/errors.c
index b8f7a2c52a..27663f1193 100644
--- a/vm/errors.c
+++ b/vm/errors.c
@@ -35,7 +35,12 @@ void throw_error(CELL error, F_STACK_FRAME *callstack_top)
 		Errors thrown from Factor code, or signal handlers, pass the
 		actual stack pointer at the time, since the saved pointer is
 		not necessarily up to date at that point. */
-		if(!callstack_top)
+		if(callstack_top)
+		{
+			callstack_top = fix_callstack_top(
+				stack_chain->callstack_bottom,callstack_top);
+		}
+		else
 			callstack_top = stack_chain->callstack_top;
 
 		throw_impl(userenv[BREAK_ENV],callstack_top);
diff --git a/vm/os-windows-nt.c b/vm/os-windows-nt.c
index f6aa314819..9a54b895b8 100644
--- a/vm/os-windows-nt.c
+++ b/vm/os-windows-nt.c
@@ -29,7 +29,7 @@ long exception_handler(PEXCEPTION_POINTERS pe)
 	CONTEXT *c = (CONTEXT*)pe->ContextRecord;
 
 	if(in_code_heap_p(c->Eip))
-		signal_callstack_top = (void *)(c->Esp - CELLS);
+		signal_callstack_top = (void *)c->Esp;
 	else
 		signal_callstack_top = NULL;