diff --git a/lib/manager/composer/artifacts.js b/lib/manager/composer/artifacts.js
index 4a34a05d9573c4733d837ba25dc199c0af69f408..7fad82bdc27a7f3efa8a543716809a6602bdf3b6 100644
--- a/lib/manager/composer/artifacts.js
+++ b/lib/manager/composer/artifacts.js
@@ -69,9 +69,11 @@ async function getArtifacts(
               platform: 'packagist',
               host,
             });
+            // istanbul ignore else
             if (hostRule) {
               // istanbul ignore else
               if (hostRule.username && hostRule.password) {
+                logger.debug('Setting packagist auth for host ' + host);
                 authJson = authJson || {};
                 authJson['http-basic'] = authJson['http-basic'] || {};
                 authJson['http-basic'][host] = {
@@ -81,6 +83,8 @@ async function getArtifacts(
               } else {
                 logger.info('Warning: unknown composer host rule type');
               }
+            } else {
+              logger.debug('No packagist auth found for host ' + host);
             }
           }
         }