diff --git a/sop-java/src/main/java/sop/Signatures.java b/sop-java/src/main/java/sop/Signatures.java
deleted file mode 100644
index dd3f000..0000000
--- a/sop-java/src/main/java/sop/Signatures.java
+++ /dev/null
@@ -1,21 +0,0 @@
-// SPDX-FileCopyrightText: 2021 Paul Schaub <vanitasvitae@fsfe.org>
-//
-// SPDX-License-Identifier: Apache-2.0
-
-package sop;
-
-import java.io.IOException;
-import java.io.OutputStream;
-
-public abstract class Signatures extends Ready {
-
-    /**
-     * Write OpenPGP signatures to the provided output stream.
-     *
-     * @param signatureOutputStream output stream
-     * @throws IOException in case of an IO error
-     */
-    @Override
-    public abstract void writeTo(OutputStream signatureOutputStream) throws IOException;
-
-}
diff --git a/sop-java/src/main/kotlin/sop/Signatures.kt b/sop-java/src/main/kotlin/sop/Signatures.kt
new file mode 100644
index 0000000..63aafe9
--- /dev/null
+++ b/sop-java/src/main/kotlin/sop/Signatures.kt
@@ -0,0 +1,19 @@
+// SPDX-FileCopyrightText: 2023 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package sop
+
+import java.io.IOException
+import java.io.OutputStream
+
+abstract class Signatures : Ready() {
+
+    /**
+     * Write OpenPGP signatures to the provided output stream.
+     *
+     * @param outputStream signature output stream
+     * @throws IOException in case of an IO error
+     */
+    @Throws(IOException::class) abstract override fun writeTo(outputStream: OutputStream)
+}