Index: configure.ac
==================================================================
--- configure.ac
+++ configure.ac
@@ -274,12 +274,15 @@
 			[Whether gcc atomic operations are available])
 		], [AC_MSG_RESULT(no)])
 
 	AC_CHECK_HEADER(libkern/OSAtomic.h, [
 		test x"$atomic_ops" = x"none" && atomic_ops="libkern/OSAtomic.h"
-		AC_DEFINE(OF_HAVE_LIBKERN_OSATOMIC_H, 1,
-			[Whether we have libkern/OSAtomic.h])])
+		AC_DEFINE(OF_HAVE_OSATOMIC, 1,
+			[Whether we have libkern/OSAtomic.h])
+		AC_CHECK_FUNC(OSAtomicAdd64Barrier, [
+			AC_DEFINE(OF_HAVE_OSATOMIC_64, 1,
+				[Whether we have OSAtomic*64])])])
 else
 	dnl We can only have one thread - therefore everything is atomic
 	atomic_ops="not needed"
 fi
 

Index: src/OFBlock.m
==================================================================
--- src/OFBlock.m
+++ src/OFBlock.m
@@ -15,10 +15,11 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
 #import "OFBlock.h"
+#import "atomic.h"
 
 /// \cond internal
 @protocol RetainRelease
 - retain;
 - (void)release;

Index: src/atomic.h
==================================================================
--- src/atomic.h
+++ src/atomic.h
@@ -7,18 +7,20 @@
  * This file is part of ObjFW. It may be distributed under the terms of the
  * Q Public License 1.0, which can be found in the file LICENSE included in
  * the packaging of this file.
  */
 
+#include <stdlib.h>
+
 #import "macros.h"
 
 #if defined(OF_THREADS) && !defined(OF_X86_ASM) && !defined(OF_AMD64_ASM) && \
-    !defined(OF_HAVE_GCC_ATOMIC_OPS) && !defined(OF_HAVE_LIBKERN_OSATOMIC_H)
+    !defined(OF_HAVE_GCC_ATOMIC_OPS) && !defined(OF_HAVE_OSATOMIC)
 # error No atomic operations available!
 #endif
 
-#ifdef OF_HAVE_LIBKERN_OSATOMIC_H
+#ifdef OF_HAVE_OSATOMIC
 # include <libkern/OSAtomic.h>
 #endif
 
 static OF_INLINE int
 of_atomic_add_int(volatile int *p, int i)
@@ -35,15 +37,17 @@
 	);
 
 	return i;
 #elif defined(OF_HAVE_GCC_ATOMIC_OPS)
 	return __sync_add_and_fetch(p, i);
-#elif defined(OF_HAVE_LIBKERN_OSATOMIC_H)
+#elif defined(OF_HAVE_OSATOMIC)
 	if (sizeof(int) == 4)
 		return OSAtomicAdd32Barrier(i, p);
+# ifdef OF_HAVE_OSATOMIC_64
 	else if (sizeof(int) == 8)
 		return OSAtomicAdd64Barrier(i, p);
+# endif
 	else
 		abort();
 #endif
 }
 
@@ -62,11 +66,11 @@
 	);
 
 	return i;
 #elif defined(OF_HAVE_GCC_ATOMIC_OPS)
 	return __sync_add_and_fetch(p, i);
-#elif defined(OF_HAVE_LIBKERN_OSATOMIC_H)
+#elif defined(OF_HAVE_OSATOMIC)
 	return OSAtomicAdd32Barrier(i, p);
 #endif
 }
 
 static OF_INLINE void*
@@ -84,15 +88,17 @@
 	);
 
 	return (void*)i;
 #elif defined(OF_HAVE_GCC_ATOMIC_OPS)
 	return __sync_add_and_fetch(p, i);
-#elif defined(OF_HAVE_LIBKERN_OSATOMIC_H)
+#elif defined(OF_HAVE_OSATOMIC)
 	if (sizeof(void*) == 4)
-		return OSAtomicAdd32Barrier(i, p);
+		return (void*)OSAtomicAdd32Barrier(i, (int32_t*)p);
+# ifdef OF_HAVE_OSATOMIC_64
 	else if (sizeof(void*) == 8)
-		return OSAtomicAdd64Barrier(i, p);
+		return (void*)OSAtomicAdd64Barrier(i, (int64_t*)p);
+# endif
 	else
 		abort();
 #endif
 }
 
@@ -112,15 +118,17 @@
 	);
 
 	return i;
 #elif defined(OF_HAVE_GCC_ATOMIC_OPS)
 	return __sync_sub_and_fetch(p, i);
-#elif defined(OF_HAVE_LIBKERN_OSATOMIC_H)
+#elif defined(OF_HAVE_OSATOMIC)
 	if (sizeof(int) == 4)
 		return OSAtomicAdd32Barrier(-i, p);
+# ifdef OF_HAVE_OSATOMIC_64
 	else if (sizeof(int) == 8)
 		return OSAtomicAdd64Barrier(-i, p);
+# endif
 	else
 		abort();
 #endif
 }
 
@@ -140,11 +148,11 @@
 	);
 
 	return i;
 #elif defined(OF_HAVE_GCC_ATOMIC_OPS)
 	return __sync_sub_and_fetch(p, i);
-#elif defined(OF_HAVE_LIBKERN_OSATOMIC_H)
+#elif defined(OF_HAVE_OSATOMIC)
 	return OSAtomicAdd32Barrier(-i, p);
 #endif
 }
 
 static OF_INLINE void*
@@ -163,15 +171,17 @@
 	);
 
 	return (void*)i;
 #elif defined(OF_HAVE_GCC_ATOMIC_OPS)
 	return __sync_sub_and_fetch(p, i);
-#elif defined(OF_HAVE_LIBKERN_OSATOMIC_H)
+#elif defined(OF_HAVE_OSATOMIC)
 	if (sizeof(void*) == 4)
-		return OSAtomicAdd32Barrier(-i, p);
+		return (void*)OSAtomicAdd32Barrier(-i, (int32_t*)p);
+# ifdef OF_HAVE_OSATOMIC_64
 	else if (sizeof(void*) == 8)
-		return OSAtomicAdd64Barrier(-i, p);
+		return (void*)OSAtomicAdd64Barrier(-i, (int64_t*)p);
+# endif
 	else
 		abort();
 #endif
 }
 
@@ -194,15 +204,17 @@
 	);
 
 	return i;
 #elif defined(OF_HAVE_GCC_ATOMIC_OPS)
 	return __sync_add_and_fetch(p, 1);
-#elif defined(OF_HAVE_LIBKERN_OSATOMIC_H)
+#elif defined(OF_HAVE_OSATOMIC)
 	if (sizeof(int) == 4)
 		return OSAtomicIncrement32Barrier(p);
+# ifdef OF_HAVE_OSATOMIC_64
 	else if (sizeof(int) == 8)
 		return OSAtomicDecrement64Barrier(p);
+# endif
 	else
 		abort();
 #endif
 }
 static OF_INLINE int32_t
@@ -224,11 +236,11 @@
 	);
 
 	return i;
 #elif defined(OF_HAVE_GCC_ATOMIC_OPS)
 	return __sync_add_and_fetch(p, 1);
-#elif defined(OF_HAVE_LIBKERN_OSATOMIC_H)
+#elif defined(OF_HAVE_OSATOMIC)
 	return OSAtomicIncrement32Barrier(p);
 #endif
 }
 
 static OF_INLINE int
@@ -250,15 +262,17 @@
 	);
 
 	return i;
 #elif defined(OF_HAVE_GCC_ATOMIC_OPS)
 	return __sync_sub_and_fetch(p, 1);
-#elif defined(OF_HAVE_LIBKERN_OSATOMIC_H)
+#elif defined(OF_HAVE_OSATOMIC)
 	if (sizeof(int) == 4)
 		return OSAtomicDecrement32Barrier(p);
+# ifdef OF_HAVE_OSATOMIC_64
 	else if (sizeof(int) == 8)
 		return OSAtomicDecrement64Barrier(p);
+# endif
 	else
 		abort();
 #endif
 }
 
@@ -281,11 +295,11 @@
 	);
 
 	return i;
 #elif defined(OF_HAVE_GCC_ATOMIC_OPS)
 	return __sync_sub_and_fetch(p, 1);
-#elif defined(OF_HAVE_LIBKERN_OSATOMIC_H)
+#elif defined(OF_HAVE_OSATOMIC)
 	return OSAtomicDecrement32Barrier(p);
 #endif
 }
 
 static OF_INLINE unsigned int
@@ -308,15 +322,17 @@
 	);
 
 	return i;
 #elif defined(OF_HAVE_GCC_ATOMIC_OPS)
 	return __sync_or_and_fetch(p, i);
-#elif defined(OF_HAVE_LIBKERN_OSATOMIC_H)
+#elif defined(OF_HAVE_OSATOMIC)
 	if (sizeof(int) == 4)
 		return OSAtomicOr32Barrier(i, p);
+# ifdef OF_HAVE_OSATOMIC_64
 	else if (sizeof(int) == 8)
 		return OSAtomicOr64Barrier(i, p);
+# endif
 	else
 		abort();
 #endif
 }
 
@@ -340,11 +356,11 @@
 	);
 
 	return i;
 #elif defined(OF_HAVE_GCC_ATOMIC_OPS)
 	return __sync_or_and_fetch(p, i);
-#elif defined(OF_HAVE_LIBKERN_OSATOMIC_H)
+#elif defined(OF_HAVE_OSATOMIC)
 	return OSAtomicOr32Barrier(i, p);
 #endif
 }
 
 static OF_INLINE unsigned int
@@ -367,15 +383,17 @@
 	);
 
 	return i;
 #elif defined(OF_HAVE_GCC_ATOMIC_OPS)
 	return __sync_and_and_fetch(p, i);
-#elif defined(OF_HAVE_LIBKERN_OSATOMIC_H)
+#elif defined(OF_HAVE_OSATOMIC)
 	if (sizeof(int) == 4)
 		return OSAtomicAnd32Barrier(i, p);
+# ifdef OF_HAVE_OSATOMIC_64
 	else if (sizeof(int) == 8)
 		return OSAtomicAnd64Barrier(i, p);
+# endif
 	else
 		abort();
 #endif
 }
 
@@ -399,11 +417,11 @@
 	);
 
 	return i;
 #elif defined(OF_HAVE_GCC_ATOMIC_OPS)
 	return __sync_and_and_fetch(p, i);
-#elif defined(OF_HAVE_LIBKERN_OSATOMIC_H)
+#elif defined(OF_HAVE_OSATOMIC)
 	return OSAtomicAnd32Barrier(i, p);
 #endif
 }
 
 static OF_INLINE unsigned int
@@ -426,15 +444,17 @@
 	);
 
 	return i;
 #elif defined(OF_HAVE_GCC_ATOMIC_OPS)
 	return __sync_xor_and_fetch(p, i);
-#elif defined(OF_HAVE_LIBKERN_OSATOMIC_H)
+#elif defined(OF_HAVE_OSATOMIC)
 	if (sizeof(int) == 4)
 		return OSAtomicXor32Barrier(i, p);
+# ifdef OF_HAVE_OSATOMIC_64
 	else (sizeof(int) == 8)
 		return OSAtomicXor64Barrier(i, p);
+# endif
 	else
 		abort();
 #endif
 }
 
@@ -458,11 +478,11 @@
 	);
 
 	return i;
 #elif defined(OF_HAVE_GCC_ATOMIC_OPS)
 	return __sync_xor_and_fetch(p, i);
-#elif defined(OF_HAVE_LIBKERN_OSATOMIC_H)
+#elif defined(OF_HAVE_OSATOMIC)
 	return OSAtomicXor32Barrier(i, p);
 #endif
 }
 
 static OF_INLINE BOOL
@@ -490,11 +510,11 @@
 	);
 
 	return r;
 #elif defined(OF_HAVE_GCC_ATOMIC_OPS)
 	return __sync_bool_compare_and_swap(p, o, n);
-#elif defined(OF_HAVE_LIBKERN_OSATOMIC_H)
+#elif defined(OF_HAVE_OSATOMIC)
 	return OSAtomicCompareAndSwapIntBarrier(o, n, p);
 #endif
 }
 
 static OF_INLINE BOOL
@@ -522,11 +542,11 @@
 	);
 
 	return r;
 #elif defined(OF_HAVE_GCC_ATOMIC_OPS)
 	return __sync_bool_compare_and_swap(p, o, n);
-#elif defined(OF_HAVE_LIBKERN_OSATOMIC_H)
+#elif defined(OF_HAVE_OSATOMIC)
 	return OSAtomicCompareAndSwap32Barrier(o, n, p);
 #endif
 }
 
 static OF_INLINE BOOL
@@ -554,9 +574,9 @@
 	);
 
 	return r;
 #elif defined(OF_HAVE_GCC_ATOMIC_OPS)
 	return __sync_bool_compare_and_swap(p, o, n);
-#elif defined(OF_HAVE_LIBKERN_OSATOMIC_H)
+#elif defined(OF_HAVE_OSATOMIC)
 	return OSAtomicCompareAndSwapPtrBarrier(o, n, p);
 #endif
 }

Index: src/objfw-defs.h.in
==================================================================
--- src/objfw-defs.h.in
+++ src/objfw-defs.h.in
@@ -5,11 +5,12 @@
 #undef OF_GNU_RUNTIME
 #undef OF_HAVE_ASPRINTF
 #undef OF_HAVE_BLOCKS
 #undef OF_HAVE_FAST_ENUMERATION
 #undef OF_HAVE_GCC_ATOMIC_OPS
-#undef OF_HAVE_LIBKERN_OSATOMIC_H
+#undef OF_HAVE_OSATOMIC
+#undef OF_HAVE_OSATOMIC_64
 #undef OF_HAVE_POLL
 #undef OF_HAVE_PROPERTIES
 #undef OF_HAVE_PTHREADS
 #undef OF_HAVE_PTHREAD_SPINLOCKS
 #undef OF_HAVE_SCHED_YIELD