diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 21dd5a294..345c09e7e 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -406,7 +406,7 @@ void EvalState::checkURI(const std::string & uri)
 
     /* If the URI is a path, then check it against allowedPaths as
        well. */
-    if (hasPrefix(uri, "/")) {
+    if (isAbsolute(uri)) {
         if (auto rootFS2 = rootFS.dynamic_pointer_cast<AllowListSourceAccessor>())
             rootFS2->checkAccess(CanonPath(uri));
         return;
diff --git a/src/libfetchers/path.cc b/src/libfetchers/path.cc
index f628e042c..340e7f4fa 100644
--- a/src/libfetchers/path.cc
+++ b/src/libfetchers/path.cc
@@ -97,7 +97,7 @@ struct PathInputScheme : InputScheme
     std::optional<std::string> isRelative(const Input & input) const
     {
         auto path = getStrAttr(input.attrs, "path");
-        if (hasPrefix(path, "/"))
+        if (isAbsolute(path))
             return std::nullopt;
         else
             return path;
diff --git a/src/libfetchers/registry.cc b/src/libfetchers/registry.cc
index 171afcea7..c18e12d23 100644
--- a/src/libfetchers/registry.cc
+++ b/src/libfetchers/registry.cc
@@ -153,7 +153,7 @@ static std::shared_ptr<Registry> getGlobalRegistry(const Settings & settings, re
             return std::make_shared<Registry>(settings, Registry::Global); // empty registry
         }
 
-        if (!hasPrefix(path, "/")) {
+        if (!isAbsolute(path)) {
             auto storePath = downloadFile(store, path, "flake-registry.json").storePath;
             if (auto store2 = store.dynamic_pointer_cast<LocalFSStore>())
                 store2->addPermRoot(storePath, getCacheDir() + "/flake-registry.json");
diff --git a/src/libflake/flake/flakeref.cc b/src/libflake/flake/flakeref.cc
index 15d1191b3..b81eb1292 100644
--- a/src/libflake/flake/flakeref.cc
+++ b/src/libflake/flake/flakeref.cc
@@ -178,7 +178,7 @@ std::pair<FlakeRef, std::string> parsePathFlakeRefWithFragment(
         }
 
     } else {
-        if (!hasPrefix(path, "/"))
+        if (!isAbsolute(path))
             throw BadURL("flake reference '%s' is not an absolute path", url);
         path = canonPath(path + "/" + getOr(query, "dir", ""));
     }
@@ -235,7 +235,7 @@ std::optional<std::pair<FlakeRef, std::string>> parseURLFlakeRef(
         auto parsed = parseURL(url);
         if (baseDir
             && (parsed.scheme == "path" || parsed.scheme == "git+file")
-            && !hasPrefix(parsed.path, "/"))
+            && !isAbsolute(parsed.path))
             parsed.path = absPath(parsed.path, *baseDir);
         return fromParsedURL(fetchSettings, std::move(parsed), isFlake);
     } catch (BadURL &) {
diff --git a/src/libutil/file-system.cc b/src/libutil/file-system.cc
index 923220fd0..a86f1ba4f 100644
--- a/src/libutil/file-system.cc
+++ b/src/libutil/file-system.cc
@@ -31,12 +31,7 @@ namespace nix {
 
 namespace fs { using namespace std::filesystem; }
 
-/**
- * Treat the string as possibly an absolute path, by inspecting the
- * start of it. Return whether it was probably intended to be
- * absolute.
- */
-static bool isAbsolute(PathView path)
+bool isAbsolute(PathView path)
 {
     return fs::path { path }.is_absolute();
 }
diff --git a/src/libutil/file-system.hh b/src/libutil/file-system.hh
index 7fdaba811..204907339 100644
--- a/src/libutil/file-system.hh
+++ b/src/libutil/file-system.hh
@@ -42,6 +42,11 @@ namespace nix {
 struct Sink;
 struct Source;
 
+/**
+ * Return whether the path denotes an absolute path.
+ */
+bool isAbsolute(PathView path);
+
 /**
  * @return An absolutized path, resolving paths relative to the
  * specified directory, or the current directory otherwise.  The path
diff --git a/src/libutil/source-accessor.cc b/src/libutil/source-accessor.cc
index aa8dcf9fd..78f038cf3 100644
--- a/src/libutil/source-accessor.cc
+++ b/src/libutil/source-accessor.cc
@@ -115,7 +115,7 @@ CanonPath SourceAccessor::resolveSymlinks(
                         throw Error("infinite symlink recursion in path '%s'", showPath(path));
                     auto target = readLink(res);
                     res.pop();
-                    if (hasPrefix(target, "/"))
+                    if (isAbsolute(target))
                         res = CanonPath::root;
                     todo.splice(todo.begin(), tokenizeString<std::list<std::string>>(target, "/"));
                 }