diff --git a/hw/ppc/ppc.c b/hw/ppc/ppc.c
index a724b0bb5e..e8127599c9 100644
--- a/hw/ppc/ppc.c
+++ b/hw/ppc/ppc.c
@@ -336,6 +336,8 @@ void store_40x_dbcr0(CPUPPCState *env, uint32_t val)
 {
     PowerPCCPU *cpu = env_archcpu(env);
 
+    qemu_mutex_lock_iothread();
+
     switch ((val >> 28) & 0x3) {
     case 0x0:
         /* No action */
@@ -353,6 +355,8 @@ void store_40x_dbcr0(CPUPPCState *env, uint32_t val)
         ppc40x_system_reset(cpu);
         break;
     }
+
+    qemu_mutex_unlock_iothread();
 }
 
 /* PowerPC 40x internal IRQ controller */