diff --git a/README.md b/README.md
index 91746ab..b848b4d 100644
--- a/README.md
+++ b/README.md
@@ -147,6 +147,9 @@ mappings:
     provider: "$1"
 ```
 
+Please note that metrics with the same name must also have the same set of
+labels names.
+
 If the default metric help text is insufficient for your needs you may use the YAML
 configuration to specify a custom help text for each mapping:
 ```yaml