Index: src/once.h
==================================================================
--- src/once.h
+++ src/once.h
@@ -24,11 +24,11 @@
 typedef pthread_once_t of_once_t;
 # define OF_ONCE_INIT PTHREAD_ONCE_INIT
 #elif defined(OF_HAVE_ATOMIC_OPS)
 typedef volatile int of_once_t;
 # define OF_ONCE_INIT 0
-#elif !defined(OF_HAVE_THREADS)
+#elif defined(OF_AMIGAOS) || !defined(OF_HAVE_THREADS)
 typedef int of_once_t;
 # define OF_ONCE_INIT 0
 #endif
 
 #ifdef __cplusplus

Index: src/once.m
==================================================================
--- src/once.m
+++ src/once.m
@@ -16,10 +16,14 @@
  */
 
 #include "config.h"
 
 #import "once.h"
+
+#ifdef OF_AMIGAOS
+# include <proto/exec.h>
+#endif
 
 #if defined(OF_HAVE_THREADS) && defined(OF_HAVE_ATOMIC_OPS)
 # import "atomic.h"
 # import "mutex.h"
 #endif
@@ -42,9 +46,19 @@
 
 		of_atomic_int_inc(control);
 	} else
 		while (*control == 1)
 			of_thread_yield();
+#elif defined(OF_AMIGAOS)
+	Forbid();
+	@try {
+		if (*control == 0) {
+			*control = 1;
+			func();
+		}
+	} @finally {
+		Permit();
+	}
 #else
 # error No of_once available
 #endif
 }