diff --git a/changelog/991.bugfix.rst b/changelog/991.bugfix.rst
new file mode 100644
index 000000000..3e21631ef
--- /dev/null
+++ b/changelog/991.bugfix.rst
@@ -0,0 +1 @@
+Fixed a memory leak when deep-copying an ``NDCube`` object or its coordinates by properly implementing ``__deepcopy__`` for ``ExtraCoords`` and ``GlobalCoords``.
diff --git a/ndcube/extra_coords/extra_coords.py b/ndcube/extra_coords/extra_coords.py
index bcbf6724d..c78dd448c 100644
--- a/ndcube/extra_coords/extra_coords.py
+++ b/ndcube/extra_coords/extra_coords.py
@@ -1,4 +1,5 @@
 import abc
+import copy
 from collections.abc import Iterable
 from functools import partial, reduce
 from numbers import Integral
@@ -155,6 +156,18 @@ def __init__(self, ndcube=None):
         # We need a reference to the parent NDCube
         self._ndcube = ndcube
 
+    def __deepcopy__(self, memo):
+
+        cls = self.__class__
+        result = cls.__new__(cls)
+        memo[id(self)] = result
+        for k, v in self.__dict__.items():
+            if k == '_ndcube':
+                setattr(result, k, None)
+            else:
+                setattr(result, k, copy.deepcopy(v, memo))
+        return result
+
     @classmethod
     def from_lookup_tables(cls, names, pixel_dimensions, lookup_tables, physical_types=None):
         """
diff --git a/ndcube/global_coords.py b/ndcube/global_coords.py
index 3514a1799..bd564eb31 100644
--- a/ndcube/global_coords.py
+++ b/ndcube/global_coords.py
@@ -88,6 +88,18 @@ def __init__(self, ndcube=None):
         self._ndcube = ndcube
         self._internal_coords = OrderedDict()
 
+    def __deepcopy__(self, memo):
+
+        cls = self.__class__
+        result = cls.__new__(cls)
+        memo[id(self)] = result
+        for k, v in self.__dict__.items():
+            if k == '_ndcube':
+                setattr(result, k, None)
+            else:
+                setattr(result, k, copy.deepcopy(v, memo))
+        return result
+
     @staticmethod
     def _convert_dropped_to_internal(dropped_dimensions):
         """