diff --git a/newsfragments/663.bugfix b/newsfragments/663.bugfix
new file mode 100644
index 000000000..c632cc50a
--- /dev/null
+++ b/newsfragments/663.bugfix
@@ -0,0 +1,2 @@
+Pilatus 4: do not invert module size (is written correctly in master file)
+
diff --git a/src/dxtbx/format/FormatNXmxEigerFilewriter.py b/src/dxtbx/format/FormatNXmxEigerFilewriter.py
index 7e8eb2924..a3e73c145 100644
--- a/src/dxtbx/format/FormatNXmxEigerFilewriter.py
+++ b/src/dxtbx/format/FormatNXmxEigerFilewriter.py
@@ -52,8 +52,10 @@ def _get_nxmx(self, fh: h5py.File):
         # data_size is reversed - we should probably be more specific in when
         # we do this, i.e. check data_size is in a list of known reversed
         # values
+        known_safe = [(1082,1035),]
         for module in nxdetector.modules:
-            module.data_size = module.data_size[::-1]
+            if not tuple(module.data_size) in known_safe:
+                module.data_size = module.data_size[::-1]
         return nxmx_obj
 
     def get_raw_data(self, index):