diff --git a/platformio/__init__.py b/platformio/__init__.py
index 78fde02c..c6e11380 100644
--- a/platformio/__init__.py
+++ b/platformio/__init__.py
@@ -14,7 +14,7 @@
 
 import sys
 
-VERSION = (3, 0, "0a7")
+VERSION = (3, 0, "0a8")
 __version__ = ".".join([str(s) for s in VERSION])
 
 __title__ = "platformio"
diff --git a/platformio/builder/tools/piolib.py b/platformio/builder/tools/piolib.py
index 104ba7ab..01f73d20 100644
--- a/platformio/builder/tools/piolib.py
+++ b/platformio/builder/tools/piolib.py
@@ -360,7 +360,7 @@ class ArduinoLibBuilder(LibBuilderBase):
             "+<*.%s>" % ext
             for ext in piotool.SRC_BUILD_EXT + piotool.SRC_HEADER_EXT
         ]
-        src_filter.append("+<utility%s>" + sep)
+        src_filter.append("+<utility%s>" % sep)
         return src_filter
 
     def is_framework_compatible(self, framework):