diff --git a/newsfragments/866.bugfix b/newsfragments/866.bugfix
new file mode 100644
index 000000000..f676107ab
--- /dev/null
+++ b/newsfragments/866.bugfix
@@ -0,0 +1 @@
+``FormatNXmxEigerFilewriter``: if dependencies missing, make some (prpbably valid) assumptions about dependencies between fast, slow pixel directions and module offset
diff --git a/src/dxtbx/nexus/__init__.py b/src/dxtbx/nexus/__init__.py
index 8dc71d88c..b760ef421 100644
--- a/src/dxtbx/nexus/__init__.py
+++ b/src/dxtbx/nexus/__init__.py
@@ -357,7 +357,7 @@ def equipment_component_key(dependency):
             # Flat detector model
 
             # Apply any rotation components of the dependency chain to the fast axis
-            assert module.fast_pixel_direction.depends_on is not None
+            # assert module.fast_pixel_direction.depends_on is not None
             fast_axis_depends_on = [
                 t
                 for t in nxmx.get_dependency_chain(
@@ -372,7 +372,7 @@ def equipment_component_key(dependency):
             fast_axis = MCSTAS_TO_IMGCIF @ R @ module.fast_pixel_direction.vector
 
             # Apply any rotation components of the dependency chain to the slow axis
-            assert module.slow_pixel_direction.depends_on is not None
+            # assert module.slow_pixel_direction.depends_on is not None
             slow_axis_depends_on = [
                 t
                 for t in nxmx.get_dependency_chain(
@@ -388,9 +388,11 @@ def equipment_component_key(dependency):
 
             # Apply all components of the dependency chain to the module offset to get the
             # dxtbx panel origin
-            dependency_chain = nxmx.get_dependency_chain(
-                module.fast_pixel_direction.depends_on
-            )
+            if module.fast_pixel_direction.depends_on is not None:
+                top = module.fast_pixel_direction.depends_on
+            else:
+                top = module.module_offset.depends_on
+            dependency_chain = nxmx.get_dependency_chain(top)
             A = nxmx.get_cumulative_transformation(dependency_chain)
 
             origin = MCSTAS_TO_IMGCIF @ (