diff --git a/TTS/tts/layers/glow_tts/monotonic_align/__init__.py b/TTS/tts/layers/glow_tts/monotonic_align/__init__.py
index 267fb7f4..a2912a98 100644
--- a/TTS/tts/layers/glow_tts/monotonic_align/__init__.py
+++ b/TTS/tts/layers/glow_tts/monotonic_align/__init__.py
@@ -2,7 +2,13 @@ import numpy as np
 import torch
 from torch.nn import functional as F
 from TTS.tts.utils.generic_utils import sequence_mask
-from TTS.tts.layers.glow_tts.monotonic_align.core import maximum_path_c
+
+try:
+    # TODO: fix pypi cython installation problem.
+    from TTS.tts.layers.glow_tts.monotonic_align.core import maximum_path_c
+    CYTHON = True
+except ModuleNotFoundError:
+    CYTHON = False
 
 
 def convert_pad_shape(pad_shape):
@@ -32,6 +38,12 @@ def generate_path(duration, mask):
 
 
 def maximum_path(value, mask):
+    if CYTHON:
+        return maximum_path_cython(value, mask)
+    return maximum_path_numpy(value, mask)
+
+
+def maximum_path_cython(value, mask):
     """ Cython optimised version.
     value: [b, t_x, t_y]
     mask: [b, t_x, t_y]
@@ -47,3 +59,45 @@ def maximum_path(value, mask):
     t_y_max = mask.sum(2)[:, 0].astype(np.int32)
     maximum_path_c(path, value, t_x_max, t_y_max)
     return torch.from_numpy(path).to(device=device, dtype=dtype)
+
+
+def maximum_path_numpy(value, mask, max_neg_val=None):
+    """
+    Monotonic alignment search algorithm
+    Numpy-friendly version. It's about 4 times faster than torch version.
+    value: [b, t_x, t_y]
+    mask: [b, t_x, t_y]
+    """
+    if max_neg_val is None:
+        max_neg_val = -np.inf  # Patch for Sphinx complaint
+    value = value * mask
+
+    device = value.device
+    dtype = value.dtype
+    value = value.cpu().detach().numpy()
+    mask = mask.cpu().detach().numpy().astype(np.bool)
+
+    b, t_x, t_y = value.shape
+    direction = np.zeros(value.shape, dtype=np.int64)
+    v = np.zeros((b, t_x), dtype=np.float32)
+    x_range = np.arange(t_x, dtype=np.float32).reshape(1, -1)
+    for j in range(t_y):
+        v0 = np.pad(v, [[0, 0], [1, 0]], mode="constant", constant_values=max_neg_val)[:, :-1]
+        v1 = v
+        max_mask = v1 >= v0
+        v_max = np.where(max_mask, v1, v0)
+        direction[:, :, j] = max_mask
+
+        index_mask = x_range <= j
+        v = np.where(index_mask, v_max + value[:, :, j], max_neg_val)
+    direction = np.where(mask, direction, 1)
+
+    path = np.zeros(value.shape, dtype=np.float32)
+    index = mask[:, :, 0].sum(1).astype(np.int64) - 1
+    index_range = np.arange(b)
+    for j in reversed(range(t_y)):
+        path[index_range, index, j] = 1
+        index = index + direction[index_range, index, j] - 1
+    path = path * mask.astype(np.float32)
+    path = torch.from_numpy(path).to(device=device, dtype=dtype)
+    return path