diff --git a/cpp/petsird_generator.cpp b/cpp/petsird_generator.cpp
index bbcdb87..923233e 100644
--- a/cpp/petsird_generator.cpp
+++ b/cpp/petsird_generator.cpp
@@ -28,7 +28,7 @@ constexpr uint32_t NUMBER_OF_ENERGY_BINS = 3;
 constexpr uint32_t NUMBER_OF_TOF_BINS = 300;
 constexpr float RADIUS = 400.F;
 constexpr std::array<float, 3> CRYSTAL_LENGTH{ 20.F, 4.F, 4.F };
-constexpr std::array<float, 3> NUM_CRYSTALS_PER_MODULE{ 2, 4, 5 };
+constexpr std::array<float, 3> NUM_CRYSTALS_PER_MODULE{ 2, 4, 7 };
 constexpr uint32_t NUM_MODULES_ALONG_RING{ 20 };
 constexpr uint32_t NUM_MODULES_ALONG_AXIS{ 2 };
 constexpr float MODULE_AXIS_SPACING{ (NUM_CRYSTALS_PER_MODULE[2] + 4) * CRYSTAL_LENGTH[2] };
@@ -72,7 +72,7 @@ get_detector_module()
                                                       { 0.0, 1.0, 0.0, (rep1 - N1 / 2) * CRYSTAL_LENGTH[1] },
                                                       { 0.0, 0.0, 1.0, (rep2 - N2 / 2) * CRYSTAL_LENGTH[2] } } };
             rep_volume.transforms.push_back(transform);
-            rep_volume.ids.push_back(rep0 + N0 * (rep1 + N1 * rep2));
+            rep_volume.ids.push_back(rep2 + N2 * (rep1 + N1 * rep0));
           }
   }
 
diff --git a/python/petsird_generator.py b/python/petsird_generator.py
index 2536a7a..b8182d0 100644
--- a/python/petsird_generator.py
+++ b/python/petsird_generator.py
@@ -18,7 +18,7 @@
 RADIUS = 400
 CRYSTAL_LENGTH = (20, 4, 4)
 # num crystals in a module
-NUM_CRYSTALS_PER_MODULE = (2, 4,5)
+NUM_CRYSTALS_PER_MODULE = (2, 4, 7)
 NUM_MODULES_ALONG_RING = 20
 NUM_MODULES_ALONG_AXIS = 2
 MODULE_AXIS_SPACING = (NUM_CRYSTALS_PER_MODULE[2] + 4) * CRYSTAL_LENGTH[2]
@@ -69,7 +69,7 @@ def get_detector_module() -> petsird.DetectorModule:
                     )
                 )
                 rep_volume.transforms.append(transform)
-                rep_volume.ids.append(rep0 + N0 * (rep1 + N1 * rep2))
+                rep_volume.ids.append(rep2 + N2 * (rep1 + N1 * rep0))
 
     return petsird.DetectorModule(
         detecting_elements=[rep_volume], detecting_element_ids=[0]