diff --git a/bigchaindb/voting.py b/bigchaindb/voting.py
index 159f631f..af12f691 100644
--- a/bigchaindb/voting.py
+++ b/bigchaindb/voting.py
@@ -7,6 +7,11 @@ to test.
 import collections
 
 
+VALID = 'valid'
+INVALID = 'invalid'
+UNDECIDED = 'undecided'
+
+
 def partition_eligible_votes(votes, eligible_voters, verify_vote_signature):
     """
     Filter votes from unknown nodes or nodes that are not listed on
@@ -92,8 +97,3 @@ def decide_votes(n_voters, n_valid, n_invalid, n_agree_prev_block):
             return VALID
         return INVALID
     return UNDECIDED
-
-
-INVALID = 'invalid'
-VALID = TX_VALID = 'valid'
-UNDECIDED = TX_UNDECIDED = 'undecided'
diff --git a/tests/test_voting.py b/tests/test_voting.py
index 67c5c284..33be2fde 100644
--- a/tests/test_voting.py
+++ b/tests/test_voting.py
@@ -5,6 +5,10 @@ from bigchaindb.voting import (count_votes, partition_eligible_votes,
                                decide_votes, INVALID, VALID, UNDECIDED)
 
 
+################################################################################
+# Tests for checking vote eligibility
+
+
 def test_partition_eligible_votes():
     nodes = list(map(Bigchain, 'abc'))
     votes = [n.vote('block', 'a', True) for n in nodes]
@@ -26,6 +30,10 @@ def test_count_votes():
     }, {})
 
 
+################################################################################
+# Tests for vote decision making
+
+
 DECISION_TESTS = [dict(
     zip(['n_voters', 'n_valid', 'n_invalid', 'n_agree_prev_block'], t))
     for t in [
@@ -59,3 +67,12 @@ def test_decide_votes_invalid(kwargs):
     assert decide_votes(**kwargs) == INVALID
     kwargs['n_invalid'] -= 1
     assert decide_votes(**kwargs) == UNDECIDED
+
+
+def test_decide_votes_checks_arguments():
+    with pytest.raises(ValueError):
+        decide_votes(n_voters=1, n_valid=2, n_invalid=0, n_agree_prev_block=0)
+    with pytest.raises(ValueError):
+        decide_votes(n_voters=1, n_valid=0, n_invalid=2, n_agree_prev_block=0)
+    with pytest.raises(ValueError):
+        decide_votes(n_voters=1, n_valid=0, n_invalid=0, n_agree_prev_block=2)