Index: configure.ac
==================================================================
--- configure.ac
+++ configure.ac
@@ -395,10 +395,18 @@
 	])
 	AC_MSG_RESULT($ac_cv_snprintf_useful_ret)
 ])
 test x"$have_asprintf" != x"yes" -a x"$ac_cv_snprintf_useful_ret" != x"yes" && \
 	AC_MSG_ERROR(No asprintf and no snprintf returning required space!)
+
+AC_CHECK_FUNC(arc4random, [
+	AC_DEFINE(OF_HAVE_ARC4RANDOM, 1, [Whether we have arc4random()])
+], [
+	AC_CHECK_FUNC(random, [
+		AC_DEFINE(OF_HAVE_RANDOM, 1, [Whether we have random()])
+	])
+])
 
 AC_CHECK_LIB(dl, dlopen, LIBS="$LIBS -ldl")
 
 AC_ARG_ENABLE(threads,
 	AS_HELP_STRING([--disable-threads], [disable thread support]))

Index: src/OFObject.h
==================================================================
--- src/OFObject.h
+++ src/OFObject.h
@@ -873,12 +873,13 @@
 #import "OFObject+Serialization.h"
 
 #ifdef __cplusplus
 extern "C" {
 #endif
+extern id of_alloc_object(Class class_, size_t extraSize, size_t extraAlignment,
+    void **extra);
 extern size_t of_pagesize;
 extern size_t of_num_cpus;
-extern id of_alloc_object(Class class_, size_t extraSize, size_t extraAlignment,
-    void **extra);
+extern uint32_t of_hash_seed;
 #ifdef __cplusplus
 }
 #endif

Index: src/OFObject.m
==================================================================
--- src/OFObject.m
+++ src/OFObject.m
@@ -24,10 +24,12 @@
 
 #include <unistd.h>
 
 #include <assert.h>
 
+#include <sys/time.h>
+
 #ifdef __QNX__
 # include <sys/syspage.h>
 #endif
 
 #import "OFObject.h"
@@ -97,10 +99,11 @@
 	Class isa;
 } alloc_failed_exception;
 
 size_t of_pagesize;
 size_t of_num_cpus;
+uint32_t of_hash_seed;
 
 #if !defined(OF_APPLE_RUNTIME) || defined(__OBJC2__)
 static void
 uncaught_exception_handler(id exception)
 {
@@ -273,10 +276,24 @@
 # ifdef _SC_NPROCESSORS_CONF
 	if ((of_num_cpus = sysconf(_SC_NPROCESSORS_CONF)) < 1)
 # endif
 		of_num_cpus = 1;
 #endif
+
+#if defined(OF_HAVE_ARC4RANDOM)
+	of_hash_seed = arc4random();
+#elif defined(OF_HAVE_RANDOM)
+	struct timeval t;
+	gettimeofday(&t, NULL);
+	srandom(t.tv_usec);
+	of_hash_seed = random();
+#else
+	struct timeval t;
+	gettimeofday(&t, NULL);
+	srand(t.tv_usec);
+	of_hash_seed = rand();
+#endif
 }
 
 + (void)initialize
 {
 }

Index: src/macros.h
==================================================================
--- src/macros.h
+++ src/macros.h
@@ -324,11 +324,11 @@
 
 #define OF_ROL(value, bits)						\
 	(((value) << ((bits) % (sizeof(value) * 8))) |			\
 	(value) >> (sizeof(value) * 8 - ((bits) % (sizeof(value) * 8))))
 
-#define OF_HASH_INIT(hash) hash = 0
+#define OF_HASH_INIT(hash) hash = of_hash_seed
 #define OF_HASH_ADD(hash, byte)		\
 	{				\
 		hash += (uint8_t)byte;	\
 		hash += (hash << 10);	\
 		hash ^= (hash >> 6);	\

Index: tests/TestsAppDelegate.m
==================================================================
--- tests/TestsAppDelegate.m
+++ tests/TestsAppDelegate.m
@@ -27,11 +27,18 @@
 # include <pspkernel.h>
 # include <pspdebug.h>
 PSP_MODULE_INFO("ObjFW Tests", 0, 0, 0);
 #endif
 
-OF_APPLICATION_DELEGATE(TestsAppDelegate)
+int
+main(int argc, char *argv[])
+{
+	/* We need deterministic hashes for tests */
+	of_hash_seed = 0;
+
+	return of_application_main(&argc, &argv, [TestsAppDelegate class]);
+}
 
 @implementation TestsAppDelegate
 - (void)outputString: (OFString*)str
 	   withColor: (int)color
 {