diff --git a/pytensor/tensor/subtensor.py b/pytensor/tensor/subtensor.py
index f3532c895a..87a62cad81 100644
--- a/pytensor/tensor/subtensor.py
+++ b/pytensor/tensor/subtensor.py
@@ -2627,6 +2627,11 @@ def as_index_variable(idx):
     idx = as_tensor_variable(idx)
     if idx.type.dtype not in discrete_dtypes:
         raise TypeError("index must be integers or a boolean mask")
+    if idx.type.dtype == "bool" and idx.type.ndim == 0:
+        raise NotImplementedError(
+            "Boolean scalar indexing not implemented. "
+            "Open an issue in https://github.com/pymc-devs/pytensor/issues if you need this behavior."
+        )
     return idx
 
 
diff --git a/pytensor/tensor/variable.py b/pytensor/tensor/variable.py
index 261a8bbc4a..145f1077d3 100644
--- a/pytensor/tensor/variable.py
+++ b/pytensor/tensor/variable.py
@@ -598,7 +598,7 @@ def is_empty_array(val):
 
     def __setitem__(self, key, value):
         raise TypeError(
-            "TensorVariable does not support item assignment. Use the output of `set` or `add` instead."
+            "TensorVariable does not support item assignment. Use the output of `x[idx].set` or `x[idx].inc` instead."
         )
 
     def take(self, indices, axis=None, mode="raise"):
diff --git a/tests/tensor/test_subtensor.py b/tests/tensor/test_subtensor.py
index aebd60de56..7b3f9af617 100644
--- a/tests/tensor/test_subtensor.py
+++ b/tests/tensor/test_subtensor.py
@@ -2228,6 +2228,11 @@ def fun(x, y):
             mode=self.mode,
         )
 
+    def test_boolean_scalar_raises(self):
+        x = vector("x")
+        with pytest.raises(NotImplementedError):
+            x[np.array(True)]
+
 
 class TestInferShape(utt.InferShapeTester):
     @staticmethod
diff --git a/tests/tensor/test_variable.py b/tests/tensor/test_variable.py
index 50c36a05fc..57e47ce064 100644
--- a/tests/tensor/test_variable.py
+++ b/tests/tensor/test_variable.py
@@ -1,3 +1,4 @@
+import re
 from copy import copy
 
 import numpy as np
@@ -444,7 +445,7 @@ def test_set_inc(self):
     def test_set_item_error(self):
         x = matrix("x")
 
-        msg = "Use the output of `set` or `add` instead."
+        msg = re.escape("Use the output of `x[idx].set` or `x[idx].inc` instead.")
         with pytest.raises(TypeError, match=msg):
             x[0] = 5
         with pytest.raises(TypeError, match=msg):