diff --git a/src/finn/transformation/fpgadataflow/insert_iodma.py b/src/finn/transformation/fpgadataflow/insert_iodma.py
index 9a797bf0243d6c4f395bb9ec50bbf675cce89cbd..67143547557a9b24b311e69cff6f885f8745cd3c 100644
--- a/src/finn/transformation/fpgadataflow/insert_iodma.py
+++ b/src/finn/transformation/fpgadataflow/insert_iodma.py
@@ -138,7 +138,7 @@ class InsertIODMA(Transformation):
                 padded_instream_width = first_node_inst.get_instream_width_padded()
                 padded_instream_bytes = padded_instream_width // 8
                 # determine the feasible interface width
-                transfer_bits = padded_instream_width * np.prod(out_folded_shape[:-1])
+                transfer_bits = padded_instream_width * np.prod(in_folded_shape[:-1])
                 intfwidth = math.gcd(transfer_bits, self.max_intfwidth)
                 assert (
                     intfwidth % 8 == 0