diff --git a/devito/data/data.py b/devito/data/data.py
index ca18006331..69bfbe80c6 100644
--- a/devito/data/data.py
+++ b/devito/data/data.py
@@ -186,8 +186,8 @@ def wrapper(data, *args, **kwargs):
                     if isinstance(i, slice) and i.step is not None and i.step < 0:
                         comm_type = index_by_index
                         break
-                    else:
-                        comm_type = serial
+                else:
+                    comm_type = serial
             else:
                 comm_type = serial
             kwargs['comm_type'] = comm_type
diff --git a/requirements.txt b/requirements.txt
index 61a9636de7..6865109d16 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,5 +1,5 @@
 pip>=9.0.1
-numpy>1.16
+numpy>1.16,<2.0
 sympy>=1.9,<1.13
 psutil>=5.1.0,<6.0
 py-cpuinfo<10
diff --git a/tests/test_adjoint.py b/tests/test_adjoint.py
index 90e4c2a32b..f5f89de22e 100644
--- a/tests/test_adjoint.py
+++ b/tests/test_adjoint.py
@@ -79,14 +79,14 @@ class TestAdjoint:
         ('layers-viscoacoustic', (20, 25), 'maxwell', 4, 2, viscoacoustic_setup),
         ('layers-viscoacoustic', (20, 25), 'maxwell', 2, 2, viscoacoustic_setup),
         # 3D Deng Mcmechan Viscoacoustic tests with varying space and equation orders
-        ('layers-viscoacoustic', (20, 25, 20), 'maxwell', 4, 1, \
-            viscoacoustic_setup),
-        ('layers-viscoacoustic', (20, 25, 20), 'maxwell', 2, 1, \
-            viscoacoustic_setup),
-        ('layers-viscoacoustic', (20, 25, 20), 'maxwell', 4, 2, \
-            viscoacoustic_setup),
-        ('layers-viscoacoustic', (20, 25, 20), 'maxwell', 2, 2, \
-            viscoacoustic_setup),
+        ('layers-viscoacoustic', (20, 25, 20), 'maxwell', 4, 1,
+         viscoacoustic_setup),
+        ('layers-viscoacoustic', (20, 25, 20), 'maxwell', 2, 1,
+         viscoacoustic_setup),
+        ('layers-viscoacoustic', (20, 25, 20), 'maxwell', 4, 2,
+         viscoacoustic_setup),
+        ('layers-viscoacoustic', (20, 25, 20), 'maxwell', 2, 2,
+         viscoacoustic_setup),
     ])
     def test_adjoint_F(self, mkey, shape, kernel, space_order, time_order, setup_func):
         """