diff --git a/src/input/ThreadInputStream.cxx b/src/input/ThreadInputStream.cxx
index 9c159f016..8487acf41 100644
--- a/src/input/ThreadInputStream.cxx
+++ b/src/input/ThreadInputStream.cxx
@@ -46,6 +46,14 @@ ThreadInputStream::Start()
 	thread.Start();
 }
 
+void
+ThreadInputStream::ThreadSeek([[maybe_unused]] offset_type new_offset)
+{
+	assert(!IsSeekable());
+
+	throw std::runtime_error{"Not seekable"};
+}
+
 inline void
 ThreadInputStream::ThreadFunc() noexcept
 {
@@ -67,6 +75,24 @@ ThreadInputStream::ThreadFunc() noexcept
 	while (!close) {
 		assert(!postponed_exception);
 
+		if (IsSeeking()) {
+			const auto seek_offset_copy = offset = seek_offset;
+			seek_offset = UNKNOWN_SIZE;
+			eof = false;
+			buffer.Clear();
+
+			try {
+				const ScopeUnlock unlock(mutex);
+				ThreadSeek(seek_offset_copy);
+			} catch (...) {
+				postponed_exception = std::current_exception();
+				InvokeOnAvailable();
+				break;
+			}
+
+			offset = seek_offset_copy;
+		}
+
 		auto w = buffer.Write();
 		if (w.empty()) {
 			wake_cond.wait(lock);
@@ -115,6 +141,14 @@ ThreadInputStream::IsAvailable() const noexcept
 	return !IsEOF() || postponed_exception;
 }
 
+void
+ThreadInputStream::Seek([[maybe_unused]] std::unique_lock<Mutex> &lock,
+			offset_type new_offset)
+{
+	seek_offset = new_offset;
+	wake_cond.notify_one();
+}
+
 size_t
 ThreadInputStream::Read(std::unique_lock<Mutex> &lock,
 			std::span<std::byte> dest)
@@ -125,6 +159,11 @@ ThreadInputStream::Read(std::unique_lock<Mutex> &lock,
 		if (postponed_exception)
 			std::rethrow_exception(postponed_exception);
 
+		if (IsSeeking()) {
+			caller_cond.wait(lock);
+			continue;
+		}
+
 		auto r = buffer.Read();
 		if (!r.empty()) {
 			size_t nbytes = std::min(dest.size(), r.size());
@@ -147,5 +186,5 @@ ThreadInputStream::IsEOF() const noexcept
 {
 	assert(!thread.IsInside());
 
-	return eof && buffer.empty();
+	return eof && buffer.empty() && !IsSeeking();
 }
diff --git a/src/input/ThreadInputStream.hxx b/src/input/ThreadInputStream.hxx
index 44f7d8da3..e76bd6c0d 100644
--- a/src/input/ThreadInputStream.hxx
+++ b/src/input/ThreadInputStream.hxx
@@ -20,8 +20,6 @@
  * another thread using the regular #InputStream API.  This class
  * manages the thread and the buffer.
  *
- * This works only for "streams": unknown length, no seeking, no tags.
- *
  * The implementation must call Stop() before its destruction
  * completes.  This cannot be done in ~ThreadInputStream() because at
  * this point, the class has been morphed back to #ThreadInputStream
@@ -50,6 +48,8 @@ class ThreadInputStream : public InputStream {
 
 	CircularBuffer<std::byte> buffer{allocation};
 
+	offset_type seek_offset = UNKNOWN_SIZE;
+
 	/**
 	 * Shall the stream be closed?
 	 */
@@ -81,6 +81,8 @@ public:
 	void Check() final;
 	bool IsEOF() const noexcept final;
 	bool IsAvailable() const noexcept final;
+	void Seek(std::unique_lock<Mutex> &lock,
+		  offset_type new_offset) final;
 	size_t Read(std::unique_lock<Mutex> &lock,
 		    std::span<std::byte> dest) override final;
 
@@ -123,6 +125,16 @@ protected:
 	 */
 	virtual std::size_t ThreadRead(std::span<std::byte> dest) = 0;
 
+	/**
+	 * The actual Seek() implementation.  This virtual method will
+	 * be called from within the thread.
+	 *
+	 * The #InputStream is not locked.
+	 *
+	 * Throws on error.
+	 */
+	virtual void ThreadSeek(offset_type new_offset);
+
 	/**
 	 * Optional deinitialization before leaving the thread.
 	 *
@@ -139,5 +151,9 @@ protected:
 	virtual void Cancel() noexcept {}
 
 private:
+	bool IsSeeking() const noexcept {
+		return seek_offset != UNKNOWN_SIZE;
+	}
+
 	void ThreadFunc() noexcept;
 };