diff --git a/services/surfaceflinger/DisplayHardware/HWComposer.cpp b/services/surfaceflinger/DisplayHardware/HWComposer.cpp
index 02c31ff..2dad005 100644
--- a/services/surfaceflinger/DisplayHardware/HWComposer.cpp
+++ b/services/surfaceflinger/DisplayHardware/HWComposer.cpp
@@ -635,6 +635,7 @@
 }
 
 status_t HWComposer::prepare() {
+    Mutex::Autolock _l(mDisplayLock);
     for (size_t i=0 ; i<mNumDisplays ; i++) {
         DisplayData& disp(mDisplayData[i]);
         if (disp.framebufferTarget) {
@@ -1145,6 +1146,7 @@
 }
 
 void HWComposer::dump(String8& result) const {
+    Mutex::Autolock _l(mDisplayLock);
     if (mHwc) {
         result.appendFormat("Hardware Composer state (version %08x):\n", hwcApiVersion(mHwc));
         result.appendFormat("  mDebugForceFakeVSync=%d\n", mDebugForceFakeVSync);
diff --git a/services/surfaceflinger/DisplayHardware/HWComposer.h b/services/surfaceflinger/DisplayHardware/HWComposer.h
index 28d8c65..cc98b4c 100644
--- a/services/surfaceflinger/DisplayHardware/HWComposer.h
+++ b/services/surfaceflinger/DisplayHardware/HWComposer.h
@@ -354,6 +354,8 @@
     // mLists[i>0] can be NULL. that display is to be ignored
     struct hwc_display_contents_1*  mLists[MAX_HWC_DISPLAYS];
     DisplayData                     mDisplayData[MAX_HWC_DISPLAYS];
+    // protect mDisplayData from races between prepare and dump
+    mutable Mutex mDisplayLock;
     size_t                          mNumDisplays;
 
     cb_context*                     mCBContext;