diff --git a/frontmatter/__init__.py b/frontmatter/__init__.py
index 04f4029..921dec9 100644
--- a/frontmatter/__init__.py
+++ b/frontmatter/__init__.py
@@ -304,7 +304,7 @@ class Post(object):
     """
 
     def __init__(
-        self, content: str, handler: BaseHandler | None = None, **metadata: object
+        self, content: str, handler: BaseHandler | None = None, /, **metadata: object
     ) -> None:
         self.content = str(content)
         self.metadata = metadata
diff --git a/tests/yaml/content-key.md b/tests/yaml/content-key.md
new file mode 100644
index 0000000..692d0e1
--- /dev/null
+++ b/tests/yaml/content-key.md
@@ -0,0 +1,5 @@
+---
+content: bad key
+---
+
+Ooops!
diff --git a/tests/yaml/content-key.result.json b/tests/yaml/content-key.result.json
new file mode 100644
index 0000000..8c84961
--- /dev/null
+++ b/tests/yaml/content-key.result.json
@@ -0,0 +1,3 @@
+{
+  "content": "Ooops!"
+}
\ No newline at end of file