diff --git a/sum.go b/sum.go
index d40b5aa..cf87bb4 100644
--- a/sum.go
+++ b/sum.go
@@ -24,7 +24,9 @@ func Sum(data []byte, code uint64, length int) (Multihash, error) {
 	}
 
 	// Feed data in.
-	hasher.Write(data)
+	if _, err := hasher.Write(data); err != nil {
+		return nil, err
+	}
 
 	return encodeHash(hasher, code, length)
 }