Index: configure.ac
==================================================================
--- configure.ac
+++ configure.ac
@@ -951,10 +951,11 @@
 	AC_MSG_CHECKING(for threads)
 
 	case "$host_os" in
 	amigaos* | morphos*)
 		AC_MSG_RESULT(Amiga)
+		have_amiga_threads="yes"
 		;;
 	mingw*)
 		AC_MSG_RESULT(WinAPI)
 		;;
 	*)
@@ -1800,11 +1801,11 @@
 	echo "features)."
 	echo
 ])
 
 AS_IF([test x"$enable_threads" != x"no" -a x"$atomic_ops" = x"none" \
-    -a x"$have_spinlocks" != x"yes"], [
+    -a x"$have_spinlocks" != x"yes" -a x"$have_amiga_threads" != x"yes"], [
 	echo
 	printf "  ** Warning: You have enabled threads, but neither atomic "
 	echo "operations nor"
 	printf "  ** spinlocks are available. Expect *very* poor performance, "
 	echo "as a mutex will"

Index: src/OFObject.m
==================================================================
--- src/OFObject.m
+++ src/OFObject.m
@@ -51,10 +51,14 @@
 #endif
 
 #ifdef OF_WINDOWS
 # include <windows.h>
 #endif
+
+#ifdef OF_AMIGAOS
+# include <proto/exec.h>
+#endif
 
 #import "OFString.h"
 
 #import "instance.h"
 #if defined(OF_HAVE_ATOMIC_OPS)
@@ -71,11 +75,11 @@
 # define of_forward_stret of_method_not_found_stret
 #endif
 
 struct pre_ivar {
 	int retainCount;
-#if !defined(OF_HAVE_ATOMIC_OPS) && defined(OF_HAVE_THREADS)
+#if !defined(OF_HAVE_ATOMIC_OPS) && !defined(OF_AMIGAOS)
 	of_spinlock_t retainCountSpinlock;
 #endif
 	struct pre_mem *firstMem, *lastMem;
 };
 
@@ -184,11 +188,11 @@
 		@throw (id)&allocFailedException;
 	}
 
 	((struct pre_ivar *)instance)->retainCount = 1;
 
-#if !defined(OF_HAVE_ATOMIC_OPS) && defined(OF_HAVE_THREADS)
+#if !defined(OF_HAVE_ATOMIC_OPS) && !defined(OF_AMIGAOS)
 	if OF_UNLIKELY (!of_spinlock_new(
 	    &((struct pre_ivar *)instance)->retainCountSpinlock)) {
 		free(instance);
 		@throw [OFInitializationFailedException
 		    exceptionWithClass: class];
@@ -1181,10 +1185,23 @@
 
 - (instancetype)retain
 {
 #if defined(OF_HAVE_ATOMIC_OPS)
 	of_atomic_int_inc(&PRE_IVARS->retainCount);
+#elif defined(OF_AMIGAOS)
+	/*
+	 * On AmigaOS, we can only have one CPU. As increasing a variable is a
+	 * single instruction on M68K, we don't need Forbid() / Permit() on
+	 * M68K.
+	 */
+# ifndef OF_AMIGAOS_M68K
+	Forbid();
+# endif
+	PRE_IVARS->retainCount++;
+# ifndef OF_AMIGAOS_M68K
+	Permit();
+# endif
 #else
 	OF_ENSURE(of_spinlock_lock(&PRE_IVARS->retainCountSpinlock));
 	PRE_IVARS->retainCount++;
 	OF_ENSURE(of_spinlock_unlock(&PRE_IVARS->retainCountSpinlock));
 #endif
@@ -1206,18 +1223,27 @@
 	if (of_atomic_int_dec(&PRE_IVARS->retainCount) <= 0) {
 		of_memory_barrier_acquire();
 
 		[self dealloc];
 	}
+#elif defined(OF_AMIGAOS)
+	int retainCount;
+
+	Forbid();
+	retainCount = --PRE_IVARS->retainCount;
+	Permit();
+
+	if (retainCount == 0)
+		[self dealloc];
 #else
-	size_t c;
+	int retainCount;
 
 	OF_ENSURE(of_spinlock_lock(&PRE_IVARS->retainCountSpinlock));
-	c = --PRE_IVARS->retainCount;
+	retainCount = --PRE_IVARS->retainCount;
 	OF_ENSURE(of_spinlock_unlock(&PRE_IVARS->retainCountSpinlock));
 
-	if (c == 0)
+	if (retainCount == 0)
 		[self dealloc];
 #endif
 }
 
 - (instancetype)autorelease