diff --git a/kartothek/serialization/_generic.py b/kartothek/serialization/_generic.py
index f7eef32f..ebd8dd5a 100644
--- a/kartothek/serialization/_generic.py
+++ b/kartothek/serialization/_generic.py
@@ -268,8 +268,6 @@ def _ensure_type_stability(array_like, value, strict_date_types, require_ordered
     array_like, array_value_type = _handle_categorical_data(array_like, require_ordered)
     array_like, array_value_type = _handle_null_arrays(array_like, value_dtype)
 
-    type_comp = (value_dtype.kind, array_value_type.kind)
-
     compatible_types = [
         # UINT and INT
         ("u", "i"),
diff --git a/kartothek/serialization/testing.py b/kartothek/serialization/testing.py
index 69605e28..56f9bf29 100644
--- a/kartothek/serialization/testing.py
+++ b/kartothek/serialization/testing.py
@@ -7,10 +7,7 @@
 
 
 def _to_binary(x):
-    x = str(x)
-    if isinstance(x, str):
-        x = x.encode("utf-8")
-    return x
+    return str(x).encode("utf-8")
 
 
 BINARY_COLUMNS = [