diff --git a/source/eventcore/driver.d b/source/eventcore/driver.d
index 62410ea..794c58f 100644
--- a/source/eventcore/driver.d
+++ b/source/eventcore/driver.d
@@ -540,6 +540,9 @@ interface EventDriverFiles {
 	*/
 	bool isValid(FileFD handle) const @nogc;
 
+	/// Determines if the given file's reference count equals one.
+	bool isUnique(FileFD descriptor) const;
+
 	/** Increments the reference count of the given file.
 	*/
 	void addRef(FileFD descriptor);
diff --git a/source/eventcore/drivers/threadedfile.d b/source/eventcore/drivers/threadedfile.d
index 2e0663c..7dc85f9 100644
--- a/source/eventcore/drivers/threadedfile.d
+++ b/source/eventcore/drivers/threadedfile.d
@@ -417,6 +417,12 @@ final class ThreadedFileEventDriver(Events : EventDriverEvents, Core : EventDriv
 		return m_files[handle.value].validationCounter == handle.validationCounter;
 	}
 
+	final override bool isUnique(FileFD handle)
+	const {
+		if (!isValid(handle)) return false;
+		return m_files[handle.value].refCount == 1;
+	}
+
 	final override void addRef(FileFD descriptor)
 	{
 		if (!isValid(descriptor)) return;
diff --git a/source/eventcore/drivers/winapi/files.d b/source/eventcore/drivers/winapi/files.d
index dcdd791..a00853f 100644
--- a/source/eventcore/drivers/winapi/files.d
+++ b/source/eventcore/drivers/winapi/files.d
@@ -309,6 +309,14 @@ final class WinAPIEventDriverFiles : EventDriverFiles {
 		return false;
 	}
 
+	override bool isUnique(FileFD handle)
+	const {
+		if (!isValid(handle)) return false;
+		if (auto ps = idToHandle(handle) in m_core.m_handles)
+			return ps.refCount == 1;
+		return false;
+	}
+
 	override void addRef(FileFD descriptor)
 	{
 		if (!isValid(descriptor)) return;