diff --git a/src/Protocol/Diaspora.php b/src/Protocol/Diaspora.php
index ffa47b1688..097ec8ddd5 100644
--- a/src/Protocol/Diaspora.php
+++ b/src/Protocol/Diaspora.php
@@ -221,6 +221,11 @@ class Diaspora
 
 		$signable_data = $msg.".".base64url_encode($type).".".base64url_encode($encoding).".".base64url_encode($alg);
 
+		if ($handle == '') {
+			logger('No author could be decoded. Discarding. Message: ' . $envelope);
+			return false;
+		}
+
 		$key = self::key($handle);
 		if ($key == '') {
 			logger("Couldn't get a key for handle " . $handle . ". Discarding.");
@@ -331,6 +336,10 @@ class Diaspora
 		}
 
 		$key = self::key($author_addr);
+		if ($key == '') {
+			logger("Couldn't get a key for handle " . $author_addr . ". Discarding.");
+			System::httpExit(400);
+		}
 
 		$verify = Crypto::rsaVerify($signed_data, $signature, $key);
 		if (!$verify) {