diff --git a/SheepShaver/src/Unix/main_unix.cpp b/SheepShaver/src/Unix/main_unix.cpp
index 3cc63481..890c3df2 100644
--- a/SheepShaver/src/Unix/main_unix.cpp
+++ b/SheepShaver/src/Unix/main_unix.cpp
@@ -232,11 +232,7 @@ static void sigill_handler(int sig, sigcontext_struct *sc);
 
 
 // From asm_linux.S
-#if EMULATED_PPC
-extern int atomic_add(int *var, int v);
-extern int atomic_and(int *var, int v);
-extern int atomic_or(int *var, int v);
-#else
+#if !EMULATED_PPC
 extern "C" void *get_toc(void);
 extern "C" void *get_sp(void);
 extern "C" void flush_icache_range(void *start, void *end);
@@ -251,6 +247,47 @@ extern void paranoia_check(void);
 #endif
 
 
+#if EMULATED_PPC
+/*
+ *  Atomic operations
+ */
+
+#if HAVE_SPINLOCKS
+static spinlock_t atomic_ops_lock = SPIN_LOCK_UNLOCKED;
+#else
+#define spin_lock(LOCK)
+#define spin_unlock(LOCK)
+#endif
+
+int atomic_add(int *var, int v)
+{
+	spin_lock(&atomic_ops_lock);
+	int ret = *var;
+	*var += v;
+	spin_unlock(&atomic_ops_lock);
+	return ret;
+}
+
+int atomic_and(int *var, int v)
+{
+	spin_lock(&atomic_ops_lock);
+	int ret = *var;
+	*var &= v;
+	spin_unlock(&atomic_ops_lock);
+	return ret;
+}
+
+int atomic_or(int *var, int v)
+{
+	spin_lock(&atomic_ops_lock);
+	int ret = *var;
+	*var |= v;
+	spin_unlock(&atomic_ops_lock);
+	return ret;
+}
+#endif
+
+
 /*
  *  Main program
  */
diff --git a/SheepShaver/src/kpx_cpu/sheepshaver_glue.cpp b/SheepShaver/src/kpx_cpu/sheepshaver_glue.cpp
index 9430ee2b..61c0057d 100644
--- a/SheepShaver/src/kpx_cpu/sheepshaver_glue.cpp
+++ b/SheepShaver/src/kpx_cpu/sheepshaver_glue.cpp
@@ -57,7 +57,7 @@ static void enter_mon(void)
 }
 
 // Enable multicore (main/interrupts) cpu emulation?
-#define MULTICORE_CPU 0
+#define MULTICORE_CPU (ASYNC_IRQ ? 1 : 0)
 
 // Enable Execute68k() safety checks?
 #define SAFE_EXEC_68K 1
@@ -604,11 +604,6 @@ void emul_ppc(uint32 entry)
  *  Handle PowerPC interrupt
  */
 
-// Atomic operations
-extern int atomic_add(int *var, int v);
-extern int atomic_and(int *var, int v);
-extern int atomic_or(int *var, int v);
-
 #if !ASYNC_IRQ
 void TriggerInterrupt(void)
 {
@@ -901,31 +896,6 @@ uint32 call_macos7(uint32 tvect, uint32 arg1, uint32 arg2, uint32 arg3, uint32 a
 	return current_cpu->execute_macos_code(tvect, sizeof(args)/sizeof(args[0]), args);
 }
 
-/*
- *  Atomic operations
- */
-
-int atomic_add(int *var, int v)
-{
-	int ret = *var;
-	*var += v;
-	return ret;
-}
-
-int atomic_and(int *var, int v)
-{
-	int ret = *var;
-	*var &= v;
-	return ret;
-}
-
-int atomic_or(int *var, int v)
-{
-	int ret = *var;
-	*var |= v;
-	return ret;
-}
-
 /*
  *  Resource Manager thunks
  */