diff --git a/clang/test/lit.cfg b/clang/test/lit.cfg
index c198dfe56874b8af6a3a7f5760d28fde3223fb55..d23a40c79b7044c0b3285f886fc48daaa0674952 100644
--- a/clang/test/lit.cfg
+++ b/clang/test/lit.cfg
@@ -200,7 +200,8 @@ def getClangBuiltinIncludeDir(clang):
     if sys.platform in ['win32'] and execute_external:
         # Don't pass dosish path separator to msys bash.exe.
         dir = dir.replace('\\', '/')
-    return dir
+    # Ensure the result is an ascii string, across Python2.5+ - Python3.
+    return str(dir.decode('ascii'))
 
 config.substitutions.append( ('%clang_cc1', '%s -cc1 -internal-isystem %s'
                               % (config.clang,