diff --git a/pandas/_libs/join.pyx b/pandas/_libs/join.pyx
index 164ed8a5c9227..5929647468785 100644
--- a/pandas/_libs/join.pyx
+++ b/pandas/_libs/join.pyx
@@ -850,17 +850,7 @@ def asof_join_nearest_on_X_by_Y(ndarray[numeric_t] left_values,
         numeric_t bdiff, fdiff
 
     # search both forward and backward
-    # TODO(cython3):
-    # Bug in beta1 preventing Cython from choosing
-    # right specialization when one fused memview is None
-    # Doesn't matter what type we choose
-    # (nothing happens anyways since it is None)
-    # GH 51640
-    if left_by_values is not None and left_by_values.dtype != object:
-        by_dtype = f"{left_by_values.dtype}_t"
-    else:
-        by_dtype = object
-    bli, bri = asof_join_backward_on_X_by_Y[f"{left_values.dtype}_t", by_dtype](
+    bli, bri = asof_join_backward_on_X_by_Y(
         left_values,
         right_values,
         left_by_values,
@@ -869,7 +859,7 @@ def asof_join_nearest_on_X_by_Y(ndarray[numeric_t] left_values,
         tolerance,
         use_hashtable
     )
-    fli, fri = asof_join_forward_on_X_by_Y[f"{left_values.dtype}_t", by_dtype](
+    fli, fri = asof_join_forward_on_X_by_Y(
         left_values,
         right_values,
         left_by_values,
diff --git a/pandas/core/reshape/merge.py b/pandas/core/reshape/merge.py
index a904f4d9fbe13..e8fd3398c4db8 100644
--- a/pandas/core/reshape/merge.py
+++ b/pandas/core/reshape/merge.py
@@ -2207,13 +2207,7 @@ def injection(obj: ArrayLike):
         else:
             # choose appropriate function by type
             func = _asof_by_function(self.direction)
-            # TODO(cython3):
-            # Bug in beta1 preventing Cython from choosing
-            # right specialization when one fused memview is None
-            # Doesn't matter what type we choose
-            # (nothing happens anyways since it is None)
-            # GH 51640
-            return func[f"{left_values.dtype}_t", object](
+            return func(
                 left_values,
                 right_values,
                 None,