diff --git a/pylops/jaxoperator.py b/pylops/jaxoperator.py
index bf00a604..5d5c40ed 100644
--- a/pylops/jaxoperator.py
+++ b/pylops/jaxoperator.py
@@ -18,8 +18,8 @@
         'the jaxoperator module run "pip install jax" or'
         '"conda install -c conda-forge jax".'
     )
-    jaxarrayin_type = None
-    jaxarrayout_type = None
+    jaxarrayin_type = Any
+    jaxarrayout_type = Any
 
 JaxTypeIn = NewType("JaxTypeIn", jaxarrayin_type)
 JaxTypeOut = NewType("JaxTypeOut", jaxarrayout_type)