diff --git a/boring-sys/build/config.rs b/boring-sys/build/config.rs
index 1671981f..28a43ccc 100644
--- a/boring-sys/build/config.rs
+++ b/boring-sys/build/config.rs
@@ -165,7 +165,7 @@ impl Env {
             opt_level: target_var("OPT_LEVEL"),
             android_ndk_home: target_var("ANDROID_NDK_HOME").map(Into::into),
             cmake_toolchain_file: target_var("CMAKE_TOOLCHAIN_FILE").map(Into::into),
-            cpp_runtime_lib: target_var("BORING_BSSL_RUST_CPPLIB").map(Into::into),
+            cpp_runtime_lib: target_var("BORING_BSSL_RUST_CPPLIB"),
         }
     }
 }