Index: src/OFThread.m
==================================================================
--- src/OFThread.m
+++ src/OFThread.m
@@ -78,11 +78,11 @@
 # import "threading.h"
 
 static of_tlskey_t threadSelfKey;
 static OFThread *mainThread;
 
-static id
+static void
 callMain(id object)
 {
 	OFThread *thread = (OFThread*)object;
 
 	if (!of_tlskey_set(threadSelfKey, thread))
@@ -108,12 +108,10 @@
 
 	objc_autoreleasePoolPop(thread->_pool);
 	[OFAutoreleasePool OF_handleThreadTermination];
 
 	[thread release];
-
-	return 0;
 }
 #endif
 
 @implementation OFThread
 #ifdef OF_HAVE_THREADS

Index: src/threading.h
==================================================================
--- src/threading.h
+++ src/threading.h
@@ -95,11 +95,11 @@
 # error of_thread_is_current not implemented!
 # error of_thread_current not implemented!
 #endif
 
 extern bool of_thread_attr_init(of_thread_attr_t *attr);
-extern bool of_thread_new(of_thread_t *thread, id (*function)(id), id data,
+extern bool of_thread_new(of_thread_t *thread, void (*function)(id), id object,
     const of_thread_attr_t *attr);
 extern void of_thread_set_name(of_thread_t thread, const char *name);
 extern bool of_thread_join(of_thread_t thread);
 extern bool of_thread_detach(of_thread_t thread);
 extern void OF_NO_RETURN of_thread_exit(void);

Index: src/threading_pthread.m
==================================================================
--- src/threading_pthread.m
+++ src/threading_pthread.m
@@ -11,10 +11,28 @@
  * Alternatively, it may be distributed under the terms of the GNU General
  * Public License, either version 2 or 3, which can be found in the file
  * LICENSE.GPLv2 or LICENSE.GPLv3 respectively included in the packaging of this
  * file.
  */
+
+struct thread_ctx {
+	void (*function)(id object);
+	id object;
+};
+
+static void*
+function_wrapper(void *data)
+{
+	struct thread_ctx *ctx = data;
+
+	pthread_cleanup_push(free, data);
+
+	ctx->function(ctx->object);
+
+	pthread_cleanup_pop(1);
+	return NULL;
+}
 
 bool
 of_thread_attr_init(of_thread_attr_t *attr)
 {
 	pthread_attr_t pattr;
@@ -50,20 +68,22 @@
 
 	return true;
 }
 
 bool
-of_thread_new(of_thread_t *thread, id (*function)(id), id data,
+of_thread_new(of_thread_t *thread, void (*function)(id), id object,
     const of_thread_attr_t *attr)
 {
 	bool ret;
 	pthread_attr_t pattr;
 
 	if (pthread_attr_init(&pattr) != 0)
 		return false;
 
 	@try {
+		struct thread_ctx *ctx;
+
 		if (attr != NULL) {
 			int policy, minPrio, maxPrio;
 			struct sched_param param;
 
 			if (attr->priority < 0 || attr->priority > 1)
@@ -87,13 +107,19 @@
 
 			if (pthread_attr_setstacksize(&pattr,
 			    attr->stackSize) != 0)
 				return false;
 		}
+
+		if ((ctx = malloc(sizeof(*ctx))) == NULL)
+			return false;
+
+		ctx->function = function;
+		ctx->object = object;
 
 		ret = (pthread_create(thread, &pattr,
-		    (void*(*)(void*))function, (__bridge void*)data) == 0);
+		    function_wrapper, ctx) == 0);
 	} @finally {
 		pthread_attr_destroy(&pattr);
 	}
 
 	return ret;

Index: src/threading_winapi.m
==================================================================
--- src/threading_winapi.m
+++ src/threading_winapi.m
@@ -24,11 +24,11 @@
 
 	return true;
 }
 
 bool
-of_thread_new(of_thread_t *thread, id (*function)(id), id data,
+of_thread_new(of_thread_t *thread, void (*function)(id), id object,
     const of_thread_attr_t *attr)
 {
 	size_t stackSize = 0;
 	int priority = 0;
 
@@ -40,11 +40,11 @@
 		    (THREAD_PRIORITY_HIGHEST - THREAD_PRIORITY_LOWEST);
 		stackSize = attr->stackSize;
 	}
 
 	*thread = CreateThread(NULL, stackSize,
-	    (LPTHREAD_START_ROUTINE)function, (__bridge void*)data, 0, NULL);
+	    (LPTHREAD_START_ROUTINE)function, (__bridge void*)object, 0, NULL);
 
 	if (thread == NULL)
 		return false;
 
 	if (priority > 0)