diff --git a/pym/builder/variables/builder.py b/pym/builder/variables/builder.py
index 6d5b47b..226b33b 100644
--- a/pym/builder/variables/builder.py
+++ b/pym/builder/variables/builder.py
@@ -135,7 +135,6 @@ class VariableClBuilderSourceFilename(Variable):
     type = "file"
     element = 'file'
     opt = ["--source"]
-    value = ""
     metavalue = "SOURCE"
     untrusted = True
 
@@ -173,6 +172,11 @@ class VariableClBuilderSourceFilename(Variable):
             fullname="%s%s" % (fullname, subname),
             build=build, ver=ver, arch=arch)
 
+    def get(self):
+        if self.Get('os_root_type') == 'livecd':
+            return '/run/initramfs/live'
+        return ""
+
 
 class VariableClBuilderSource(ReadonlyVariable):
     """
@@ -473,7 +477,7 @@ class VariableClBuilderNewId(BaseBuildId):
     def check(self, value):
         if not value and self.Get('cl_builder_source_filename'):
             raise VariableError(_("Please specify the id"))
-        if not re.match("^[A-Za-z][A-Za-z0-9/:_-]+$", value):
+        if value and not re.match("^[A-Za-z][A-Za-z0-9/:_-]+$", value):
             raise VariableError(_("Wrong symbols in build ID"))
         if value in self.Get('cl_builder_storage'):
             raise VariableError(_("Assemble %s already exists")%value)