diff --git a/Project.toml b/Project.toml
index e0490035c..ce6ef2777 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,7 +1,7 @@
 name = "JUDI"
 uuid = "f3b833dc-6b2e-5b9c-b940-873ed6319979"
 authors = ["Philipp Witte, Mathias Louboutin"]
-version = "3.3.8"
+version = "3.3.9"
 
 [deps]
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"
diff --git a/src/pysource/propagators.py b/src/pysource/propagators.py
index 21a9f9e4c..109b6b760 100644
--- a/src/pysource/propagators.py
+++ b/src/pysource/propagators.py
@@ -95,11 +95,11 @@ def gradient(model, residual, rcv_coords, u, return_op=False, space_order=8, fw=
     """
     # Setting adjoint wavefieldgradient
     v = wavefield(model, space_order, fw=not fw)
-    if as_tuple(u)[0].indices[0].is_Conditional:
+    try:
         t_sub = as_tuple(u)[0].indices[0]._factor
         if isinstance(t_sub, Constant):
             t_sub = t_sub.data
-    else:
+    except AttributeError:
         t_sub = 1
 
     # Setup gradient wrt m