diff --git a/mallard/client.py b/mallard/client.py
index 82accde..f47b2b7 100644
--- a/mallard/client.py
+++ b/mallard/client.py
@@ -133,6 +133,9 @@ async def on_ready(self):
         logger.info("Ready! \U0001f986")
 
     def _clean(self, message) -> Optional[str]:
+        """
+        Filter mention from query
+        """
         if message.author == self.user:
             return None
         if not message.content:
diff --git a/mallard/config.py b/mallard/config.py
index 4a1ec21..674423d 100644
--- a/mallard/config.py
+++ b/mallard/config.py
@@ -13,7 +13,7 @@
 import yaml
 
 
-def load_config(path):
+def load_config(path) -> dict:
     with open(path, "r") as fh:
         obj = yaml.safe_load(fh)
 
diff --git a/mallard/util.py b/mallard/util.py
index 2e959fd..5e3a2c9 100644
--- a/mallard/util.py
+++ b/mallard/util.py
@@ -10,12 +10,21 @@
 # WITHOUT ANY WARRANTY. See the LICENSE file for more details.
 #
 
+import logging
 
-def plural(n) -> str:
+logger = logging.getLogger("mallard")
+
+
+def plural(n: int) -> Optional[str]:
     if n == 1:
         return ""
-    else:
+    elif n > 0:
         return "s"
+    else:
+        logger.error("plural() passed value: %d, n should be a positive integer", n)
+        raise ValueError(
+            "n must be a positive integer"
+        )  # this will actuall never happen
 
 
 class DummyGuild: