diff --git a/trieste/space.py b/trieste/space.py
index 0de9214b5..04b95fad1 100644
--- a/trieste/space.py
+++ b/trieste/space.py
@@ -656,12 +656,20 @@ def one_hot_encoder(self) -> EncoderFunction:
 
         def binary_encoder(x: TensorType) -> TensorType:
             # no need to one-hot encode binary categories (but we should still validate)
-            tf.debugging.Assert(tf.reduce_all((x == 0) | (x == 1)), [tf.constant([])])
+            tf.debugging.Assert(
+                tf.reduce_all((x == 0) | (x == 1)),
+                ["Invalid binary values for one-hot encoding:", x],
+            )
             return x
 
         def encoder(x: TensorType) -> TensorType:
             flat_x, unflatten = flatten_leading_dims(x)
-            tf.debugging.assert_equal(flat_x.shape[-1], len(self.tags))
+            tf.debugging.assert_equal(
+                flat_x.shape[-1],
+                len(self.tags),
+                message="Invalid input for one-hot encoding: "
+                f"expected {len(self.tags)} tags, got {flat_x.shape[-1]}",
+            )
             columns = tf.split(flat_x, flat_x.shape[-1], axis=1)
             encoders = [
                 (