diff --git a/inc/external-fetch.php b/inc/external-fetch.php
index b124f6e5..87160e58 100644
--- a/inc/external-fetch.php
+++ b/inc/external-fetch.php
@@ -66,7 +66,7 @@ function fetch_external ( $bind_id, $min_age, $ua_string )
       curl_setopt ( $curl, CURLOPT_TIMECONDITION, CURL_TIMECOND_IFMODSINCE );
       if ( isset( $ua_string ) )
         curl_setopt($curl, CURLOPT_USERAGENT, $ua_string);
-      dbg_error_log("external", "checking external resource for remote changes " . $row->external_url );
+      dbg_error_log("external", "checking external resource for remote changes %s ", $row->external_url );
       $ics = curl_exec ( $curl );
       $info = curl_getinfo ( $curl );
       if ( $info['http_code'] === 304 || (isset($info['filetime']) && $info['filetime'] != -1 && new DateTime("@" . $info['filetime']) <=  $local_ts )) {
@@ -80,7 +80,7 @@ function fetch_external ( $bind_id, $min_age, $ua_string )
       dbg_error_log("external", "external resource changed, re importing" . $info['filetime'] );
     }
     else {
-      dbg_error_log("external", "fetching external resource for the first time " . $row->external_url );
+      dbg_error_log("external", "fetching external resource for the first time %s ", $row->external_url );
     }
     curl_setopt ( $curl, CURLOPT_NOBODY, false );
     curl_setopt ( $curl, CURLOPT_HEADER, false );