diff --git a/docs/source/changelog.rst b/docs/source/changelog.rst
index 2cb975ee..920d2572 100644
--- a/docs/source/changelog.rst
+++ b/docs/source/changelog.rst
@@ -24,6 +24,13 @@ Planar Imaging
   ROIs. This result will also be included in the ``results_data`` structure.
   This is not done for light/rad phantoms.
 
+Picket Fence
+^^^^^^^^^^^^
+
+* The Halcyon MLC configurations were incorrect and have now been fixed. Thanks to Dominic Rafferty for
+  pointing this out. Previously, it was using a similar configuration as the TrueBeam out of lack of experience
+  with the system. The new configuration was based on `this paper <https://aapm.onlinelibrary.wiley.com/doi/pdf/10.1002/acm2.12568>`__.
+
 Winston-Lutz
 ^^^^^^^^^^^^
 
diff --git a/pylinac/picketfence.py b/pylinac/picketfence.py
index 2f5f20e4..69d19bed 100644
--- a/pylinac/picketfence.py
+++ b/pylinac/picketfence.py
@@ -105,13 +105,15 @@ class MLC(enum.Enum):
         "name": "MLCi",
         "arrangement": MLCArrangement([(40, 10)]),
     }  #:
+    # Halcyon reference
+    # https://aapm.onlinelibrary.wiley.com/doi/pdf/10.1002/acm2.12568
     HALCYON_DISTAL = {
         "name": "Halcyon distal",
-        "arrangement": MLCArrangement([(60, 5)], offset=2.5),
+        "arrangement": MLCArrangement([(28, 10)]),
     }  #:
     HALCYON_PROXIMAL = {
         "name": "Halcyon proximal",
-        "arrangement": MLCArrangement([(60, 5)]),
+        "arrangement": MLCArrangement([(29, 10)]),
     }  #:
 
 
diff --git a/tests_basic/test_picketfence.py b/tests_basic/test_picketfence.py
index c9e7cc91..dbbd180f 100644
--- a/tests_basic/test_picketfence.py
+++ b/tests_basic/test_picketfence.py
@@ -73,7 +73,7 @@ def test_custom_MLC_arrangement(self):
     def test_all_mlc_arrangements(self):
         """This isn't really testing the MLCs so much as a constancy check to ensure they haven't changed."""
         path = get_file_from_cloud_test_repo([TEST_DIR, "AS500_PF.dcm"])
-        expected_max_error = [0.13, 0.18, 0.16, 0.14, 0.06, 0.14, 0.14]
+        expected_max_error = [0.13, 0.18, 0.16, 0.14, 0.06, 0.06, 0.06]
         for max_error, mlc in zip(expected_max_error, MLC):
             pf = PicketFence(path, mlc=mlc)
             pf.analyze()
@@ -809,6 +809,22 @@ class ChicagoError(PFTestMixin, TestCase):
     max_error = 0.3
 
 
+class HalcyonProximal(PFTestMixin, TestCase):
+    file_name = "Distal - DoRa - Really proximal.dcm"
+    mlc = "Halcyon proximal"
+    max_error = 0.13
+    num_pickets = 6
+    mean_picket_spacing = 50
+
+
+class HalcyonDistal(PFTestMixin, TestCase):
+    file_name = "Proximal - DoRa - Really distal.dcm"
+    mlc = "Halcyon distal"
+    max_error = 0.13
+    num_pickets = 6
+    mean_picket_spacing = 50
+
+
 @skip
 class CharlestonRA(PFTestMixin, TestCase):
     file_name = ["Charleston", "TB1", "July2016", "RA.dcm"]