diff --git a/core/java/android/hardware/camera2/CameraCaptureSession.java b/core/java/android/hardware/camera2/CameraCaptureSession.java
index 0cf8df130cd4c..aeddf032a176d 100644
--- a/core/java/android/hardware/camera2/CameraCaptureSession.java
+++ b/core/java/android/hardware/camera2/CameraCaptureSession.java
@@ -114,6 +114,11 @@ public abstract class CameraCaptureSession implements AutoCloseable {
      * the Surface provided to prepare must not be used as a target of a CaptureRequest submitted
      * to this session.</p>
      *
+     * <p>{@link android.hardware.camera2.CameraCharacteristics#INFO_SUPPORTED_HARDWARE_LEVEL_LEGACY LEGACY}
+     * devices cannot pre-allocate output buffers; for those devices,
+     * {@link StateCallback#onSurfacePrepared} will be immediately called, and no preallocation is
+     * done.</p>
+     *
      * @param surface the output Surface for which buffers should be pre-allocated. Must be one of
      * the output Surfaces used to create this session.
      *
diff --git a/core/java/android/hardware/camera2/legacy/CameraDeviceUserShim.java b/core/java/android/hardware/camera2/legacy/CameraDeviceUserShim.java
index abe26ead2170f..edad00fe4fe7e 100644
--- a/core/java/android/hardware/camera2/legacy/CameraDeviceUserShim.java
+++ b/core/java/android/hardware/camera2/legacy/CameraDeviceUserShim.java
@@ -202,6 +202,7 @@ public class CameraDeviceUserShim implements ICameraDeviceUser {
         private static final int CAMERA_IDLE = 1;
         private static final int CAPTURE_STARTED = 2;
         private static final int RESULT_RECEIVED = 3;
+        private static final int PREPARED = 4;
 
         private final HandlerThread mHandlerThread;
         private Handler mHandler;
@@ -253,7 +254,9 @@ public class CameraDeviceUserShim implements ICameraDeviceUser {
 
         @Override
         public void onPrepared(int streamId) {
-            // TODO
+            Message msg = getHandler().obtainMessage(PREPARED,
+                    /*arg1*/ streamId, /*arg2*/ 0);
+            getHandler().sendMessage(msg);
         }
 
         @Override
@@ -301,6 +304,11 @@ public class CameraDeviceUserShim implements ICameraDeviceUser {
                             mCallbacks.onResultReceived(result, resultExtras);
                             break;
                         }
+                        case PREPARED: {
+                            int streamId = msg.arg1;
+                            mCallbacks.onPrepared(streamId);
+                            break;
+                        }
                         default:
                             throw new IllegalArgumentException(
                                 "Unknown callback message " + msg.what);
@@ -631,7 +639,9 @@ public class CameraDeviceUserShim implements ICameraDeviceUser {
             return CameraBinderDecorator.ENODEV;
         }
 
-        // TODO: Implement and fire callback
+        // LEGACY doesn't support actual prepare, just signal success right away
+        mCameraCallbacks.onPrepared(streamId);
+
         return CameraBinderDecorator.NO_ERROR;
     }