diff --git a/libhwcomposer/hwc.cpp b/libhwcomposer/hwc.cpp
index 9bf0c45..7bfbf06 100644
--- a/libhwcomposer/hwc.cpp
+++ b/libhwcomposer/hwc.cpp
@@ -158,7 +158,9 @@
 
 static int hwc_prepare_external(hwc_composer_device_1 *dev,
         hwc_display_contents_1_t *list, int dpy) {
+
     hwc_context_t* ctx = (hwc_context_t*)(dev);
+    Locker::Autolock _l(ctx->mExtLock);
 
     if (LIKELY(list && list->numHwLayers > 1) &&
             ctx->dpyAttr[dpy].isActive &&
@@ -398,7 +400,7 @@
 {
     ATRACE_CALL();
     int ret = 0;
-    Locker::Autolock _l(ctx->mExtSetLock);
+    Locker::Autolock _l(ctx->mExtLock);
 
     if (LIKELY(list) && ctx->dpyAttr[dpy].isActive &&
         !ctx->dpyAttr[dpy].isPause &&