diff --git a/sigal/image.py b/sigal/image.py
index 3568d2c..f4e6c91 100644
--- a/sigal/image.py
+++ b/sigal/image.py
@@ -256,7 +256,7 @@ def get_exif_tags(data):
         exptime = data['ExposureTime']
         if isinstance(exptime, tuple):
             try:
-                simple['exposure'] = exptime[0] / exptime[1]
+                simple['exposure'] = exptime[0] / float(exptime[1])
             except IndexError:
                 # Pillow >= 3.0
                 simple['exposure'] = exptime[0]