diff --git a/crisprbact/predict.py b/crisprbact/predict.py
index f0e09b8c99b57f5c2b31407070dbff2d46b8a1d3..0c395ebefe923bf5f408259311d96f355ea2d55b 100644
--- a/crisprbact/predict.py
+++ b/crisprbact/predict.py
@@ -12,6 +12,7 @@ with open_binary("crisprbact", "reg_coef.pkl") as handle:
     coef = np.load(handle, allow_pickle=True)
 
 bases = ["A", "T", "G", "C"]
+GUIDE_LEN = 20
 
 
 def encode(seq):
@@ -40,7 +41,7 @@ def find_targets(seq):
             guide_start = start - start_min
             guide_end = end - 16 - 3
             guide = seq_revcomp[guide_start:guide_end]
-            assert len(guide) == 20
+            assert len(guide) == GUIDE_LEN
             pos_seq_start = L - guide_end
             pos_seq_stop = L - guide_start
             pos_seq_pam = pos_seq_start - 3
@@ -62,7 +63,7 @@ def get_strand_value(value):
     return strand_dict[str(value)]
 
 
-def on_target_predict(seq, genome=None, seed_sizes=[8, 9, 10, 11, 12]):
+def on_target_predict(seq, genome=None, seed_sizes=[8, 9, 10, 11, 12, GUIDE_LEN]):
 
     seq = seq.upper()  # make uppercase
     seq = re.sub(r"\s", "", seq)  # removes white space