--- a/python/mozbuild/mozbuild/mach_commands.py
+++ b/python/mozbuild/mozbuild/mach_commands.py
@@ -1743,30 +1743,27 @@ class PackageFrontend(MachCommandBase):
                         for task in tasks
                     }
 
             toolchains = tasks('toolchain')
 
             for b in from_build:
                 user_value = b
 
-                if '/' not in b:
-                    b = '{}/opt'.format(b)
-
                 if not b.startswith('toolchain-'):
                     b = 'toolchain-{}'.format(b)
 
                 task = toolchains.get(b)
                 if not task:
                     self.log(logging.ERROR, 'artifact', {'build': user_value},
                              'Could not find a toolchain build named `{build}`')
                     return 1
 
-                optimized, task_id = optimize_task(task, {})
-                if not optimized:
+                task_id = optimize_task(task, {})
+                if task_id in (True, False):
                     self.log(logging.ERROR, 'artifact', {'build': user_value},
                              'Could not find artifacts for a toolchain build '
                              'named `{build}`')
                     return 1
 
                 for artifact in list_artifacts(task_id):
                     name = artifact['name']
                     if not name.startswith('public/'):