diff --git a/src/xrt/auxiliary/tracking/t_tracker_slam.cpp b/src/xrt/auxiliary/tracking/t_tracker_slam.cpp
index ee1b6efcc..17610804c 100644
--- a/src/xrt/auxiliary/tracking/t_tracker_slam.cpp
+++ b/src/xrt/auxiliary/tracking/t_tracker_slam.cpp
@@ -1380,20 +1380,29 @@ receive_frame(TrackerSlam &t, struct xrt_frame *frame, uint32_t cam_index)
 	default: SLAM_ERROR("Unknown image format"); return;
 	}
 
+	xrt_hand_masks_sample hand_masks{};
 	{
 		unique_lock lock(t.last_hand_masks_mutex);
-		for (auto &view : t.last_hand_masks.views) {
-			if (!view.enabled) {
+		hand_masks = t.last_hand_masks;
+	}
+
+	auto &view = hand_masks.views[cam_index];
+	std::vector<vit_mask_t> masks;
+	if (view.enabled) {
+		for (auto &hand : view.hands) {
+			if (!hand.enabled) {
 				continue;
 			}
+			vit_mask_t mask{};
+			mask.x = hand.rect.x;
+			mask.y = hand.rect.y;
+			mask.w = hand.rect.w;
+			mask.h = hand.rect.h;
+			masks.push_back(mask);
+		}
 
-			for (auto &hand : view.hands) {
-				if (!hand.enabled) {
-					continue;
-				}
-				// TODO@mateosss: add_mask(hand.rect);
-			}
-		};
+		sample.mask_count = masks.size();
+		sample.masks = masks.empty() ? nullptr : masks.data();
 	}
 
 	{
diff --git a/src/xrt/include/xrt/xrt_defines.h b/src/xrt/include/xrt/xrt_defines.h
index ad9628c4a..2689faf65 100644
--- a/src/xrt/include/xrt/xrt_defines.h
+++ b/src/xrt/include/xrt/xrt_defines.h
@@ -391,6 +391,18 @@ struct xrt_rect
 	struct xrt_size extent;
 };
 
+/*!
+ * Image rectangle
+ *
+ * @todo Unify xrt_rect and xrt_rect_f32 field names
+ *
+ * @ingroup xrt_iface math
+ */
+struct xrt_rect_f32
+{
+	float x, y, w, h;
+};
+
 /*!
  * Normalized image rectangle, coordinates and size in 0 .. 1 range.
  *
diff --git a/src/xrt/include/xrt/xrt_tracking.h b/src/xrt/include/xrt/xrt_tracking.h
index e7dc38162..b63b245f3 100644
--- a/src/xrt/include/xrt/xrt_tracking.h
+++ b/src/xrt/include/xrt/xrt_tracking.h
@@ -149,8 +149,8 @@ struct xrt_hand_masks_sample
 		bool enabled; //!< Whether any hand mask for this camera is being reported
 		struct xrt_hand_masks_sample_hand
 		{
-			bool enabled;         //!< Whether a mask for this hand is being reported
-			struct xrt_rect rect; //!< The mask itself in pixel coordinates
+			bool enabled;             //!< Whether a mask for this hand is being reported
+			struct xrt_rect_f32 rect; //!< The mask itself in pixel coordinates
 		} hands[2];
 	} views[XRT_TRACKING_MAX_SLAM_CAMS];
 };
diff --git a/src/xrt/tracking/hand/mercury/hg_sync.cpp b/src/xrt/tracking/hand/mercury/hg_sync.cpp
index d2cf25869..c21e2317b 100644
--- a/src/xrt/tracking/hand/mercury/hg_sync.cpp
+++ b/src/xrt/tracking/hand/mercury/hg_sync.cpp
@@ -572,12 +572,10 @@ predict_new_regions_of_interest(struct HandTracking *hgt)
 				hroi.provenance = ROIProvenance::POSE_PREDICTION;
 				hroi.found = true;
 
-				xrt_vec2 &center = hroi.center_px;
-				float &size = hroi.size_px;
-				masks_hand.rect.offset.w = int(center.x - size / 2);
-				masks_hand.rect.offset.h = int(center.y - size / 2);
-				masks_hand.rect.extent.w = int(size);
-				masks_hand.rect.extent.h = int(size);
+				const float SCALER = 1.25f;
+				float s = hroi.size_px * SCALER;
+				xrt_vec2 &c = hroi.center_px;
+				masks_hand.rect = xrt_rect_f32{c.x - s / 2, c.y - s / 2, s, s};
 				masks_hand.enabled = true;
 			} else {
 				hroi.found = false;