diff --git a/pgpainless-core/src/main/java/org/pgpainless/key/OpenPgpV4Fingerprint.java b/pgpainless-core/src/main/java/org/pgpainless/key/OpenPgpV4Fingerprint.java
index 35cf7471..c77a25bf 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/key/OpenPgpV4Fingerprint.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/key/OpenPgpV4Fingerprint.java
@@ -129,6 +129,7 @@ public class OpenPgpV4Fingerprint implements CharSequence, Comparable<OpenPgpV4F
     }
 
     @Override
+    @Nonnull
     public String toString() {
         return fingerprint;
     }