diff --git a/src/fs/AllocatedPath.hxx b/src/fs/AllocatedPath.hxx
index c345470c8..e3281b77f 100644
--- a/src/fs/AllocatedPath.hxx
+++ b/src/fs/AllocatedPath.hxx
@@ -252,7 +252,7 @@ public:
 	void ChopSeparators();
 
 	gcc_pure
-	bool IsAbsolute() {
+	bool IsAbsolute() const {
 		return PathTraitsFS::IsAbsolute(c_str());
 	}
 };
diff --git a/src/fs/Path.hxx b/src/fs/Path.hxx
index 4a3ae815f..084b7c335 100644
--- a/src/fs/Path.hxx
+++ b/src/fs/Path.hxx
@@ -158,7 +158,7 @@ public:
 	}
 
 	gcc_pure
-	bool IsAbsolute() {
+	bool IsAbsolute() const {
 		return PathTraitsFS::IsAbsolute(c_str());
 	}
 };