diff --git a/boot.php b/boot.php
index 13e1e17936..85e1598831 100644
--- a/boot.php
+++ b/boot.php
@@ -945,6 +945,11 @@ function unxmlify($s) {
 
 if(! function_exists('hex2bin')) {
 function hex2bin($s) {
+	if(! ctype_xdigit($s)) {
+		logger('hex2bin: illegal input: ' . print_r(debug_backtrace(), true));
+		return($s);
+	}
+
 	return(pack("H*",$s));
 }}
 
diff --git a/include/items.php b/include/items.php
index beed024a1c..1fdbc6fc20 100644
--- a/include/items.php
+++ b/include/items.php
@@ -788,8 +788,8 @@ function dfrn_deliver($owner,$contact,$atom) {
 		return (($res->status) ? $res->status : 3);
 
 	$postvars     = array();
-	$sent_dfrn_id = hex2bin($res->dfrn_id);
-	$challenge    = hex2bin($res->challenge);
+	$sent_dfrn_id = hex2bin((string) $res->dfrn_id);
+	$challenge    = hex2bin((string) $res->challenge);
 	$rino_allowed = ((intval($res->rino) === 1) ? 1 : 0);
 
 	$final_dfrn_id = '';
diff --git a/include/poller.php b/include/poller.php
index 28e421f5fe..fc45ff9c3e 100644
--- a/include/poller.php
+++ b/include/poller.php
@@ -186,8 +186,8 @@
 
 			$postvars = array();
 
-			$sent_dfrn_id = hex2bin($res->dfrn_id);
-			$challenge    = hex2bin($res->challenge);
+			$sent_dfrn_id = hex2bin((string) $res->dfrn_id);
+			$challenge    = hex2bin((string) $res->challenge);
 
 			$final_dfrn_id = '';