diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index e18648557..9edd69c64 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -196,16 +196,16 @@ std::string_view baseNameOf(std::string_view path)
 }
 
 
-bool isInDir(const Path & path, const Path & dir)
+bool isInDir(std::string_view path, std::string_view dir)
 {
-    return path[0] == '/'
-        && string(path, 0, dir.size()) == dir
+    return path.substr(0, 1) == "/"
+        && path.substr(0, dir.size()) == dir
         && path.size() >= dir.size() + 2
         && path[dir.size()] == '/';
 }
 
 
-bool isDirOrInDir(const Path & path, const Path & dir)
+bool isDirOrInDir(std::string_view path, std::string_view dir)
 {
     return path == dir || isInDir(path, dir);
 }
diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index d08f42826..dfad33ed2 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -66,11 +66,13 @@ Path dirOf(const Path & path);
    following the final `/' (trailing slashes are removed). */
 std::string_view baseNameOf(std::string_view path);
 
-/* Check whether 'path' is a descendant of 'dir'. */
-bool isInDir(const Path & path, const Path & dir);
+/* Check whether 'path' is a descendant of 'dir'. Both paths must be
+   canonicalized. */
+bool isInDir(std::string_view path, std::string_view dir);
 
-/* Check whether 'path' is equal to 'dir' or a descendant of 'dir'. */
-bool isDirOrInDir(const Path & path, const Path & dir);
+/* Check whether 'path' is equal to 'dir' or a descendant of
+   'dir'. Both paths must be canonicalized. */
+bool isDirOrInDir(std::string_view path, std::string_view dir);
 
 /* Get status of `path'. */
 struct stat lstat(const Path & path);