diff --git a/.travis.yml b/.travis.yml
index 286243c..94df0a3 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -9,6 +9,7 @@ install:
 
 script:
   - nosetests --with-coverage --cover-package=stegano
+  - mypy --ignore-missing-imports --follow-imports skip --check-untyped-defs stegano/
 
 after_success:
   - coveralls
diff --git a/stegano/steganalysis/statistics.py b/stegano/steganalysis/statistics.py
index d3e622e..60ff72f 100644
--- a/stegano/steganalysis/statistics.py
+++ b/stegano/steganalysis/statistics.py
@@ -37,16 +37,17 @@ def steganalyse(img):
     """
     encoded = img.copy()
     width, height = img.size
-    colours = Counter()
+    colours_counter = Counter() # type: Counter[int]
     for row in range(height):
         for col in range(width):
             r, g, b = img.getpixel((col, row))
-            colours[r] += 1
+            colours_counter[r] += 1
 
-    most_common = colours.most_common(10)
-    dict_colours = OrderedDict(sorted(list(colours.items()), key=lambda t: t[1]))
+    most_common = colours_counter.most_common(10)
+    dict_colours = OrderedDict(sorted(list(colours_counter.items()),
+                                key=lambda t: t[1]))
 
-    colours = 0
+    colours = 0 # type: float
     for colour in list(dict_colours.keys()):
         colours += colour
     colours = colours / len(dict_colours)