diff --git a/src/fs/AllocatedPath.hxx b/src/fs/AllocatedPath.hxx
index 577dfa073..e2ff53cbd 100644
--- a/src/fs/AllocatedPath.hxx
+++ b/src/fs/AllocatedPath.hxx
@@ -295,6 +295,10 @@ public:
 		return Traits::Relative(c_str(), other_fs.c_str());
 	}
 
+	/**
+	 * Returns the filename extension (excluding the dot) or
+	 * nullptr if the path does not have one.
+	 */
 	[[gnu::pure]]
 	const_pointer GetExtension() const noexcept {
 		return Path{*this}.GetExtension();
diff --git a/src/fs/Path.hxx b/src/fs/Path.hxx
index a8a0ac9b2..fceb5c3b5 100644
--- a/src/fs/Path.hxx
+++ b/src/fs/Path.hxx
@@ -166,6 +166,10 @@ public:
 		return Traits::IsAbsolute(c_str());
 	}
 
+	/**
+	 * Returns the filename extension (excluding the dot) or
+	 * nullptr if the path does not have one.
+	 */
 	[[gnu::pure]]
 	const_pointer GetExtension() const noexcept;
 };