diff --git a/bochs/iodev/display/voodoo.cc b/bochs/iodev/display/voodoo.cc
index ab217e12d..bc02d7a93 100644
--- a/bochs/iodev/display/voodoo.cc
+++ b/bochs/iodev/display/voodoo.cc
@@ -166,19 +166,19 @@ BX_THREAD_FUNC(cmdfifo_thread, indata)
   while (1) {
 #ifdef WIN32
     if (WaitForSingleObject(v->fbi.cmdfifo[0].event, 1) == WAIT_OBJECT_0) {
-      BX_LOCK(cmdfifo_mutex);
       while (v->fbi.cmdfifo[0].enable && (v->fbi.cmdfifo[0].depth >= v->fbi.cmdfifo[0].depth_needed)) {
         cmdfifo_process();
       }
+      BX_LOCK(cmdfifo_mutex);
       v->fbi.cmdfifo[0].cmd_ready = 0;
       BX_UNLOCK(cmdfifo_mutex);
     }
 #else
     while (!v->fbi.cmdfifo[0].event) BX_MSLEEP(1);
-    BX_LOCK(cmdfifo_mutex);
     while (v->fbi.cmdfifo[0].enable && (v->fbi.cmdfifo[0].depth >= v->fbi.cmdfifo[0].depth_needed)) {
       cmdfifo_process();
     }
+    BX_LOCK(cmdfifo_mutex);
     v->fbi.cmdfifo[0].cmd_ready = 0;
     v->fbi.cmdfifo[0].event = 0;
     BX_UNLOCK(cmdfifo_mutex);
@@ -614,7 +614,9 @@ void bx_voodoo_c::vertical_timer_handler(void *this_ptr)
 #ifdef WIN32
     SetEvent(v->fbi.cmdfifo[0].event);
 #else
+    BX_LOCK(cmdfifo_mutex);
     v->fbi.cmdfifo[0].event = 1;
+    BX_UNLOCK(cmdfifo_mutex);
 #endif
   }
 
diff --git a/bochs/iodev/display/voodoo_func.h b/bochs/iodev/display/voodoo_func.h
index cdafd36ed..3e4adbd57 100644
--- a/bochs/iodev/display/voodoo_func.h
+++ b/bochs/iodev/display/voodoo_func.h
@@ -2406,7 +2406,9 @@ Bit32u cmdfifo_calc_depth_needed(void)
 
   if (v->fbi.cmdfifo[0].depth == 0)
     return needed;
+  BX_LOCK(cmdfifo_mutex);
   command = *(Bit32u*)(&v->fbi.ram[v->fbi.cmdfifo[0].rdptr & v->fbi.mask]);
+  BX_UNLOCK(cmdfifo_mutex);
   type = (Bit8u)(command & 0x07);
   switch (type) {
     case 0:
@@ -2461,7 +2463,9 @@ void cmdfifo_w(Bit32u fbi_offset, Bit32u data)
   *(Bit32u*)(&v->fbi.ram[fbi_offset]) = data;
   v->fbi.cmdfifo[0].depth++;
   if (v->fbi.cmdfifo[0].depth_needed == BX_MAX_BIT32U) {
+    BX_UNLOCK(cmdfifo_mutex);
     v->fbi.cmdfifo[0].depth_needed = cmdfifo_calc_depth_needed();
+    BX_LOCK(cmdfifo_mutex);
   }
   if (v->fbi.cmdfifo[0].depth >= v->fbi.cmdfifo[0].depth_needed) {
     v->fbi.cmdfifo[0].cmd_ready = 1;
@@ -2473,9 +2477,11 @@ Bit32u cmdfifo_r(void)
 {
   Bit32u data;
 
+  BX_LOCK(cmdfifo_mutex);
   data = *(Bit32u*)(&v->fbi.ram[v->fbi.cmdfifo[0].rdptr & v->fbi.mask]);
   v->fbi.cmdfifo[0].rdptr += 4;
   v->fbi.cmdfifo[0].depth--;
+  BX_UNLOCK(cmdfifo_mutex);
   return data;
 }