diff --git a/skimage/util/dtype.py b/skimage/util/dtype.py
index da2ff5e7..11199cc8 100644
--- a/skimage/util/dtype.py
+++ b/skimage/util/dtype.py
@@ -120,7 +120,7 @@ def _convert(image, dtype):
             # int8 -> uint32
             image = dtype(image)
             image *= 2**16 + 2**8 + 1
-        result += image
+        result += dtype(image)
         return result
     if kind == 'i':
         # signed integer -> signed integer