diff --git a/.travis.yml b/.travis.yml
index d3b53c0..1fb4fef 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -3,7 +3,6 @@ sudo: false
 language: python
 python:
 - '2.7'
-- '3.3'
 - '3.4'
 - '3.5'
 env: COMPILER_NAME=gcc CXX=g++-5 CC=gcc-5
diff --git a/hlatyper.py b/hlatyper.py
index 22d8820..e1b76ec 100644
--- a/hlatyper.py
+++ b/hlatyper.py
@@ -623,7 +623,7 @@ def calculate_coverage(alignment, features, alleles_to_plot, features_used):
                     pairing_info.loc[reads][allele]):
                 if not i_pairing:
                     continue  # or i_pairing = 4. Happens if one end maps to the allele but a different allele has a full paired hit.
-                coverage[bool(i_mismatches)][i_pairing-1][i_hitcount-1][i_pos-1:i_pos-1+i_read_length] += 1
+                coverage[int(bool(i_mismatches))][i_pairing-1][i_hitcount-1][i_pos-1:i_pos-1+i_read_length] += 1
 
         coverage_matrices.append((allele, coverage))
     return coverage_matrices