diff --git a/dap/algos/peakfind.py b/dap/algos/peakfind.py
index c4ef8e5..a706cb9 100644
--- a/dap/algos/peakfind.py
+++ b/dap/algos/peakfind.py
@@ -54,8 +54,8 @@ def calc_peakfinder_analysis(results, data, pixel_mask):
     results["number_of_spots"] = number_of_spots
 
     # to coordinates where position of first pixel/point is (1, 1)
-    results["spot_x"] = peak_list_x + 0.5
-    results["spot_y"] = peak_list_y + 0.5
+    results["spot_x"] = [x + 0.5 for x in peak_list_x]
+    results["spot_y"] = [y + 0.5 for y in peak_list_y]
     results["spot_intensity"] = copy(peak_list_value) #TODO: why is this copy needed?
 
     npeaks_threshold_hit = results.get("npeaks_threshold_hit", 15)