diff --git a/Makefile b/Makefile
index 8178e00..631f595 100644
--- a/Makefile
+++ b/Makefile
@@ -1,10 +1,15 @@
-CFLAGS = -g -Wall
+ifeq ($(shell uname), Darwin)
+	APPLE_CCFLAGS = -m64
+	APPLE_ASFLAGS = -arch x86_64
+endif
 
-gttest: gthr.o swtch.o
-	$(CC) -o $@ $^
+CFLAGS = $(APPLE_CCFLAGS) -g -Wall
+
+gttest: gthr.o gtswtch.o
+	$(CC) $(APPLE_CCFLAGS) -o $@ $^
 
 .S.o:
-	as -o $@ $^
+	as $(APPLE_ASFLAGS) -o $@ $^
 
 .PHONY: clean
 clean:
diff --git a/gthr.c b/gthr.c
index 18fc4c1..b017680 100644
--- a/gthr.c
+++ b/gthr.c
@@ -23,18 +23,16 @@ struct gt {
 		Unused,
 		Running,
 		Ready,
-		Zombie,
 	} st;
-	int excode;
 };
 
 struct gt gttbl[MaxGThreads];
 struct gt *gtcur;
-bool gttick;
 
+void gtinit(void);
 void gtret(int ret);
 void gtswtch(struct gtctx *old, struct gtctx *new);
-bool gtyield(bool force);
+bool gtyield(void);
 static void gtstop(void);
 int gtgo(void (*f)(void));
 
@@ -49,25 +47,21 @@ void __attribute__((noreturn))
 gtret(int ret)
 {
 	if (gtcur != &gttbl[0]) {
-		gtcur->st = Zombie;
-		gtcur->excode = ret;
-		gtyield(true);
+		gtcur->st = Unused;
+		gtyield();
 		assert(!"reachable");
 	}
-	while (gtyield(true))
+	while (gtyield())
 		;
 	exit(ret);
 }
 
 bool
-gtyield(bool force)
+gtyield(void)
 {
 	struct gt *p;
 	struct gtctx *old, *new;
 
-	if (!gttick && !force)
-		return false;
-	gttick = 0;
 	p = gtcur;
 	while (p->st != Ready) {
 		if (++p == &gttbl[MaxGThreads])
@@ -76,7 +70,7 @@ gtyield(bool force)
 			return false;
 	}
 
-	if (gtcur->st != Zombie)
+	if (gtcur->st != Unused)
 		gtcur->st = Ready;
 	p->st = Running;
 	old = &gtcur->ctx;
@@ -114,7 +108,7 @@ gtgo(void (*f)(void))
 }
 
 
-/* Now we test this nice library. */
+/* Now, let's run some simple threaded code. */
 
 void
 f(void)
@@ -125,7 +119,7 @@ f(void)
 	id = ++x;
 	for (i = 0; i < 10; i++) {
 		printf("%d %d\n", id, i);
-		gtyield(true);
+		gtyield();
 	}
 }
 
diff --git a/swtch.S b/gtswtch.S
similarity index 94%
rename from swtch.S
rename to gtswtch.S
index 5899b5a..c747da2 100644
--- a/swtch.S
+++ b/gtswtch.S
@@ -5,8 +5,8 @@
 #   %rsi contains the context to switch to.
 #
 
-.code64
-.globl gtswtch
+.globl _gtswtch, gtswtch
+_gtswtch:
 gtswtch:
 
         mov     %rsp, 0x00(%rdi)