diff --git a/pgpainless-core/src/main/java/org/pgpainless/key/util/KeyIdUtil.java b/pgpainless-core/src/main/java/org/pgpainless/key/util/KeyIdUtil.java
index 7ebac8fd..78e03f71 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/key/util/KeyIdUtil.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/key/util/KeyIdUtil.java
@@ -32,6 +32,6 @@ public final class KeyIdUtil {
     }
 
     public static String formatKeyId(long keyId) {
-        return Long.toHexString(keyId).toUpperCase();
+        return String.format("%016X", keyId);
     }
 }
diff --git a/pgpainless-core/src/test/java/org/pgpainless/key/util/KeyIdUtilTest.java b/pgpainless-core/src/test/java/org/pgpainless/key/util/KeyIdUtilTest.java
new file mode 100644
index 00000000..f85bd43f
--- /dev/null
+++ b/pgpainless-core/src/test/java/org/pgpainless/key/util/KeyIdUtilTest.java
@@ -0,0 +1,41 @@
+// SPDX-FileCopyrightText: 2023 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package org.pgpainless.key.util;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class KeyIdUtilTest {
+
+    @Test
+    public void testParsing() {
+        String longKeyId = "b1bd1f049ec87f3d"; // we parse from lowercase, but formatting will produce uppercase
+        long asLong = KeyIdUtil.fromLongKeyId(longKeyId);
+        assertEquals(-5639317053693722819L, asLong);
+        assertEquals(longKeyId.toUpperCase(), KeyIdUtil.formatKeyId(-5639317053693722819L));
+    }
+
+    @Test
+    public void testParsingLowerAndUppercase() {
+        long fromLower = KeyIdUtil.fromLongKeyId("f5ffdf6d71dd5789");
+        assertEquals(-720611754201229431L, fromLower);
+        long fromUpper = KeyIdUtil.fromLongKeyId("F5FFDF6D71DD5789");
+        assertEquals(-720611754201229431L, fromUpper);
+    }
+
+    @Test
+    public void formatLowerAsUpper() {
+        assertEquals("5F04ACF44FD822B1", KeyIdUtil.formatKeyId(KeyIdUtil.fromLongKeyId("5f04acf44fd822b1")));
+    }
+
+    @Test
+    public void testParsing0() {
+        long asLong = 0L;
+        String formatted = KeyIdUtil.formatKeyId(asLong);
+        assertEquals("0000000000000000", formatted);
+        assertEquals(asLong, KeyIdUtil.fromLongKeyId("0000000000000000"));
+    }
+}