diff --git a/vm/callstack.cpp b/vm/callstack.cpp
index ce4d242119..f2ad5096c8 100755
--- a/vm/callstack.cpp
+++ b/vm/callstack.cpp
@@ -24,19 +24,30 @@ void factor_vm::dispatch_signal_handler(cell *sp, cell *pc, cell newpc)
 	that don't create a stack frame will be out of alignment by sizeof(cell)
 	bytes. */
 	cell offset = *sp % 16;
-	if (offset != 0)
-		fatal_error("fault in unaligned frame at", *pc);
-
-	/* Nonleaf procedure */
-	cell newsp = *sp - sizeof(cell);
-	*sp = newsp;
-	*(cell*)newsp = *pc;
-	*pc = newpc;
-	ctx->callstack_top = (stack_frame*)newsp;
-
-	/* XXX handle leaf procedure */
+	if (offset == 0) {
+		signal_from_leaf = false;
+		cell newsp = *sp - sizeof(cell);
+		*sp = newsp;
+		*(cell*)newsp = *pc;
+		*pc = newpc;
+		ctx->callstack_top = (stack_frame*)newsp;
+	} else if (offset == 16 - sizeof(cell)) {
+		dispatch_signal_handler_from_leaf(sp, pc, newpc);
+	} else {
+		fatal_error("Invalid stack frame during signal handler", *sp);
+	}
 }
 
+void factor_vm::dispatch_signal_handler_from_leaf(cell *sp, cell *pc, cell newpc)
+{
+	/* We should try to conjure a stack frame here, but we may need to deal
+	with callstack overflows or the GC moving code around.
+	For now leave the stack untouched so the signal handler returns into
+	the parent procedure. This will cause things to blow up if the stack
+	is left unbalanced. */
+	signal_from_leaf = true;
+	*pc = newpc;
+}
 
 /* We ignore the two topmost frames, the 'callstack' primitive
 frame itself, and the frame calling the 'callstack' primitive,
diff --git a/vm/errors.cpp b/vm/errors.cpp
index c57e7832f7..1b5fe221f1 100755
--- a/vm/errors.cpp
+++ b/vm/errors.cpp
@@ -179,9 +179,11 @@ void factor_vm::enqueue_safepoint_sample()
 
 void factor_vm::handle_safepoint()
 {
+	if (signal_from_leaf)
+		std::cout << "XXX SIGNALED FROM LEAF\n";
+
 	if (safepoint_fep) {
-		std::cout << "Interrupted. Entering low-level debugger...\n";
-		std::cout << "\n";
+		std::cout << "Interrupted\n";
 		factorbug();
 		code->unguard_safepoint();
 		safepoint_fep = false;
diff --git a/vm/vm.hpp b/vm/vm.hpp
index b7373b3951..180b92b3c5 100755
--- a/vm/vm.hpp
+++ b/vm/vm.hpp
@@ -56,6 +56,7 @@ struct factor_vm
 
 	/* Global variables used to pass fault handler state from signal handler
 	to VM */
+	bool signal_from_leaf;
 	cell signal_number;
 	cell signal_fault_addr;
 	unsigned int signal_fpu_status;
@@ -605,6 +606,7 @@ struct factor_vm
 	void primitive_callstack_bounds();
 	template<typename Iterator> void iterate_callstack(context *ctx, Iterator &iterator);
 	void dispatch_signal_handler(cell *sp, cell *pc, cell newpc);
+	void dispatch_signal_handler_from_leaf(cell *sp, cell *pc, cell newpc);
 
 	template<typename CellA, typename CellB, typename CellC>
 	void dispatch_signal_handler(CellA *sp, CellB *pc, CellC newpc)