diff --git a/src/SPC/builder/unix/library/ngtcp2.php b/src/SPC/builder/unix/library/ngtcp2.php
index e256f813..8ea280a8 100644
--- a/src/SPC/builder/unix/library/ngtcp2.php
+++ b/src/SPC/builder/unix/library/ngtcp2.php
@@ -53,6 +53,6 @@ trait ngtcp2
         // on macOS, the static library may contain other static libraries?
         // ld: archive member 'libssl.a' not a mach-o file in libngtcp2_crypto_ossl.a
         shell()->cd(BUILD_LIB_PATH)
-            ->exec("ar -t libngtcp2_crypto_ossl.a | grep '\.a$' | xargs -n1 ar d libngtcp2_crypto_ossl.a");
+            ->exec("ar -t libngtcp2_crypto_ossl.a | grep '\\.a$' | xargs -n1 ar d libngtcp2_crypto_ossl.a");
     }
 }