diff --git a/colbert/indexing/faiss.py b/colbert/indexing/faiss.py
index c0d55642..f52e118b 100644
--- a/colbert/indexing/faiss.py
+++ b/colbert/indexing/faiss.py
@@ -37,11 +37,11 @@ def load_sample(samples_paths, sample_fraction=None):
     return sample
 
 
-def prepare_faiss_index(slice_samples_paths, partitions, sample_fraction=None):
+def prepare_faiss_index(slice_samples_paths, partitions, m=16, sample_fraction=None):
     training_sample = load_sample(slice_samples_paths, sample_fraction=sample_fraction)
 
     dim = training_sample.shape[-1]
-    index = FaissIndex(dim, partitions)
+    index = FaissIndex(dim, partitions, m)
 
     print_message("#> Training with the vectors...")
 
@@ -84,7 +84,7 @@ def index_faiss(args):
 
         assert not os.path.exists(output_path), output_path
 
-        index = prepare_faiss_index(slice_samples_paths, args.partitions, args.sample)
+        index = prepare_faiss_index(slice_samples_paths, args.partitions, args.m, args.sample)
 
         loaded_parts = queue.Queue(maxsize=1)
 
diff --git a/colbert/indexing/faiss_index.py b/colbert/indexing/faiss_index.py
index 7bb3a50d..4e3c5ab7 100644
--- a/colbert/indexing/faiss_index.py
+++ b/colbert/indexing/faiss_index.py
@@ -11,9 +11,10 @@
 
 
 class FaissIndex():
-    def __init__(self, dim, partitions):
+    def __init__(self, dim, partitions, m=16):
         self.dim = dim
         self.partitions = partitions
+        self.m = m
 
         self.gpu = FaissIndexGPU()
         self.quantizer, self.index = self._create_index()
@@ -21,7 +22,7 @@ def __init__(self, dim, partitions):
 
     def _create_index(self):
         quantizer = faiss.IndexFlatL2(self.dim)  # faiss.IndexHNSWFlat(dim, 32)
-        index = faiss.IndexIVFPQ(quantizer, self.dim, self.partitions, 16, 8)
+        index = faiss.IndexIVFPQ(quantizer, self.dim, self.partitions, self.m, 8)
 
         return quantizer, index
 
diff --git a/colbert/utils/parser.py b/colbert/utils/parser.py
index 7acda986..5d95e12e 100644
--- a/colbert/utils/parser.py
+++ b/colbert/utils/parser.py
@@ -78,6 +78,7 @@ def add_index_use_input(self):
         self.add_argument('--index_root', dest='index_root', required=True)
         self.add_argument('--index_name', dest='index_name', required=True)
         self.add_argument('--partitions', dest='partitions', default=None, type=int)
+        self.add_argument('--m', dest='m', default=16, type=int)
 
     def add_retrieval_input(self):
         self.add_index_use_input()