diff --git a/moo/kernel/System.moo b/moo/kernel/System.moo
index 260049c..73736bd 100644
--- a/moo/kernel/System.moo
+++ b/moo/kernel/System.moo
@@ -183,7 +183,7 @@ class System(Apex)
 			nil.
 		]
 		ensure: [
-			| pid proc |
+			| pid proc oldps |
 
 			// stop subscribing to signals.
 			os_intr_sem signal.
@@ -193,9 +193,9 @@ class System(Apex)
 
 			// this disables autonomous process switching only. 
 			// TODO: check if the ensure block code can trigger process switching?
-			//       whap happens if the ensure block creates new processes? this is likely to affect the termination loop below.
+			//       what happens if the ensure block creates new processes? this is likely to affect the termination loop below.
 			//       even the id of the terminated process may get reused.... 
-			self _disableProcessSwitching. 
+			oldps := self _toggleProcessSwitching: false.
 
 			/*
 			 0 -> startup  <--- this should also be stored in the 'caller' variable.
@@ -214,7 +214,7 @@ class System(Apex)
 
 			System logNl: 'Requesting to terminate the caller process of id ' & (caller id) asString.
 			caller terminate.  // terminate the startup process.
-			self _enableProcessSwitching.
+			self _toggleProcessSwitching: oldps.
 
 			System logNl: '>>>>End of OS signal handler process ' & (thisProcess id) asString.
 
@@ -229,8 +229,7 @@ class System(Apex)
 	method(#class,#primitive) _getSigfd.
 	method(#class,#primitive) _setSig: signo.
 	method(#class,#primitive) _halting.
-	method(#class,#primitive) _enableProcessSwitching.
-	method(#class,#primitive) _disableProcessSwitching.
+	method(#class,#primitive) _toggleProcessSwitching: v.
 	method(#class,#primitive,#lenient) _findProcessById: id.
 	method(#class,#primitive,#lenient) _findProcessByIdGreaterThan: id.
 
diff --git a/moo/lib/exec.c b/moo/lib/exec.c
index 7d71897..1826afd 100644
--- a/moo/lib/exec.c
+++ b/moo/lib/exec.c
@@ -3260,17 +3260,26 @@ static moo_pfrc_t pf_system_return_value_to_context (moo_t* moo, moo_mod_t* mod,
 }
 
 /* ------------------------------------------------------------------ */
-static moo_pfrc_t pf_system_enable_process_switching (moo_t* moo, moo_mod_t* mod, moo_ooi_t nargs)
+static moo_pfrc_t pf_system_toggle_process_switching (moo_t* moo, moo_mod_t* mod, moo_ooi_t nargs)
 {
-	moo->no_proc_switch = 0;
-	MOO_STACK_SETRETTORCV (moo, nargs);
-	return MOO_PF_SUCCESS;
-}
+	moo_oop_t v;
+	int oldnps;
 
-static moo_pfrc_t pf_system_disable_process_switching (moo_t* moo, moo_mod_t* mod, moo_ooi_t nargs)
-{
-	moo->no_proc_switch = 0;
-	MOO_STACK_SETRETTORCV (moo, nargs);
+	oldnps = moo->no_proc_switch;
+
+	v = MOO_STACK_GETARG(moo, nargs, 0);
+	if (v == moo->_false)
+	{
+		/* disable process switching */
+		moo->no_proc_switch = 1;
+	}
+	else
+	{
+		/* enable process switching */
+		moo->no_proc_switch = 0;
+	}
+
+	MOO_STACK_SETRET (moo, nargs, (oldnps? moo->_false: moo->_true));
 	return MOO_PF_SUCCESS;
 }
 
@@ -4465,8 +4474,6 @@ static pf_t pftab[] =
 	{ "System_calloc",                         { moo_pf_system_calloc,                    1, 1 } },
 	{ "System_calloc:",                        { moo_pf_system_calloc,                    1, 1 } },
 	{ "System_collectGarbage",                 { moo_pf_system_collect_garbage,           0, 0 } },
-	{ "System_disableProcessSwitching",        { pf_system_disable_process_switching,     0, 0 } },
-	{ "System_enableProcessSwitching",         { pf_system_enable_process_switching,      0, 0 } },
 	{ "System_findProcessById:",               { pf_system_find_process_by_id,            1, 1 } },
 	{ "System_findProcessByIdGreaterThan:",    { pf_system_find_process_by_id_gt,         1, 1 } },
 	{ "System_free",                           { moo_pf_system_free,                      1, 1 } },
@@ -4499,6 +4506,7 @@ static pf_t pftab[] =
 	{ "System_putUint8",                       { moo_pf_system_put_uint8,                 3, 3 } },
 	{ "System_return:to:",                     { pf_system_return_value_to_context,       2, 2 } },
 	{ "System_setSig:",                        { moo_pf_system_set_sig,                   1, 1 } },
+	{ "System_toggleProcessSwitching:",        { pf_system_toggle_process_switching,      1, 1 } },
 
 	{ "_dump",                                 { pf_dump,                                 0, MA } },