diff --git a/bitbake/lib/bb/utils.py b/bitbake/lib/bb/utils.py
index d299b2efdb..068b631c94 100644
--- a/bitbake/lib/bb/utils.py
+++ b/bitbake/lib/bb/utils.py
@@ -759,7 +759,7 @@ def mkdirhier(directory):
     """Create a directory like 'mkdir -p', but does not complain if
     directory already exists like os.makedirs
     """
-    if directory.find('${') != -1:
+    if '${' in str(directory):
         bb.fatal("Directory name {} contains unexpanded bitbake variable. This may cause build failures and WORKDIR polution.".format(directory))
     try:
         os.makedirs(directory)