Index: src/mutex.h
==================================================================
--- src/mutex.h
+++ src/mutex.h
@@ -18,11 +18,11 @@
 #include "objfw-defs.h"
 
 #include "platform.h"
 
 #if !defined(OF_HAVE_THREADS) || \
-    (!defined(OF_HAVE_PTHREADS) && !defined(OF_WINDOWS))
+    (!defined(OF_HAVE_PTHREADS) && !defined(OF_WINDOWS) && !defined(OF_AMIGAOS))
 # error No mutexes available!
 #endif
 
 #import "macros.h"
 
@@ -30,10 +30,13 @@
 # include <pthread.h>
 typedef pthread_mutex_t of_mutex_t;
 #elif defined(OF_WINDOWS)
 # include <windows.h>
 typedef CRITICAL_SECTION of_mutex_t;
+#elif defined(OF_AMIGAOS)
+# include <exec/semaphores.h>
+typedef struct SignalSemaphore of_mutex_t;
 #endif
 
 #if defined(OF_HAVE_ATOMIC_OPS)
 # import "atomic.h"
 typedef volatile int of_spinlock_t;
@@ -46,13 +49,15 @@
 
 #ifdef OF_HAVE_SCHED_YIELD
 # include <sched.h>
 #endif
 
-#if defined(OF_HAVE_RECURSIVE_PTHREAD_MUTEXES) || defined(OF_WINDOWS)
+#if defined(OF_HAVE_RECURSIVE_PTHREAD_MUTEXES) || defined(OF_WINDOWS) || \
+    defined(OF_AMIGAOS)
 # define of_rmutex_t of_mutex_t
 #else
+# import "tlskey.h"
 typedef struct {
 	of_mutex_t mutex;
 	of_tlskey_t count;
 } of_rmutex_t;
 #endif

Index: src/mutex.m
==================================================================
--- src/mutex.m
+++ src/mutex.m
@@ -21,13 +21,16 @@
 
 #if defined(OF_HAVE_PTHREADS)
 # include "mutex_pthread.m"
 #elif defined(OF_WINDOWS)
 # include "mutex_winapi.m"
+#elif defined(OF_AMIGAOS)
+# include "mutex_amiga.m"
 #endif
 
-#if !defined(OF_HAVE_RECURSIVE_PTHREAD_MUTEXES) && !defined(OF_WINDOWS)
+#if !defined(OF_HAVE_RECURSIVE_PTHREAD_MUTEXES) && !defined(OF_WINDOWS) && \
+    !defined(OF_AMIGAOS)
 bool
 of_rmutex_new(of_rmutex_t *rmutex)
 {
 	if (!of_mutex_new(&rmutex->mutex))
 		return false;

ADDED   src/mutex_amiga.m
Index: src/mutex_amiga.m
==================================================================
--- src/mutex_amiga.m
+++ src/mutex_amiga.m
@@ -0,0 +1,84 @@
+/*
+ * Copyright (c) 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017,
+ *               2018, 2019
+ *   Jonathan Schleifer <js@heap.zone>
+ *
+ * All rights reserved.
+ *
+ * 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.QPL included in
+ * the packaging of this file.
+ *
+ * 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.
+ */
+
+#include <proto/exec.h>
+
+bool
+of_mutex_new(of_mutex_t *mutex)
+{
+	InitSemaphore(mutex);
+
+	return true;
+}
+
+bool
+of_mutex_lock(of_mutex_t *mutex)
+{
+	ObtainSemaphore(mutex);
+
+	return true;
+}
+
+bool
+of_mutex_trylock(of_mutex_t *mutex)
+{
+	return AttemptSemaphore(mutex);
+}
+
+bool
+of_mutex_unlock(of_mutex_t *mutex)
+{
+	ReleaseSemaphore(mutex);
+
+	return true;
+}
+
+bool
+of_mutex_free(of_mutex_t *mutex)
+{
+	return true;
+}
+
+bool
+of_rmutex_new(of_rmutex_t *rmutex)
+{
+	return of_mutex_new(rmutex);
+}
+
+bool
+of_rmutex_lock(of_rmutex_t *rmutex)
+{
+	return of_mutex_lock(rmutex);
+}
+
+bool
+of_rmutex_trylock(of_rmutex_t *rmutex)
+{
+	return of_mutex_trylock(rmutex);
+}
+
+bool
+of_rmutex_unlock(of_rmutex_t *rmutex)
+{
+	return of_mutex_unlock(rmutex);
+}
+
+bool
+of_rmutex_free(of_rmutex_t *rmutex)
+{
+	return of_mutex_free(rmutex);
+}