diff --git a/adb_utils_test.cpp b/adb_utils_test.cpp
index aabc5d7..9daa397 100644
--- a/adb_utils_test.cpp
+++ b/adb_utils_test.cpp
@@ -111,7 +111,7 @@
   EXPECT_EQ("/system/bin", adb_dirname("/system/bin/sh/"));
 }
 
-void test_mkdirs(const std::string basepath) {
+void test_mkdirs(const std::string& basepath) {
   // Test creating a directory hierarchy.
   EXPECT_TRUE(mkdirs(basepath));
   // Test finding an existing directory hierarchy.