diff --git a/graphics/s2/files/patch-src_s2_util_math_exactfloat_exactfloat.cc b/graphics/s2/files/patch-src_s2_util_math_exactfloat_exactfloat.cc
index fd6dfaec318c..111df840b8f0 100644
--- a/graphics/s2/files/patch-src_s2_util_math_exactfloat_exactfloat.cc
+++ b/graphics/s2/files/patch-src_s2_util_math_exactfloat_exactfloat.cc
@@ -1,11 +1,13 @@
+Reference:	https://github.com/google/s2geometry/commit/7a40135059545396237a0199c558d749fe3be0b1
+
 --- src/s2/util/math/exactfloat/exactfloat.cc.orig	2022-05-24 22:12:24 UTC
 +++ src/s2/util/math/exactfloat/exactfloat.cc
 @@ -141,7 +141,7 @@ inline static uint64 BN_ext_get_uint64(const BIGNUM* b
  #ifdef IS_LITTLE_ENDIAN
    S2_CHECK_EQ(BN_bn2lebinpad(bn, reinterpret_cast<unsigned char*>(&r),
                sizeof(r)), sizeof(r));
 -#elif IS_BIG_ENDIAN
 +#elif defined(IS_BIG_ENDIAN)
    S2_CHECK_EQ(BN_bn2binpad(bn, reinterpret_cast<unsigned char*>(&r),
                sizeof(r)), sizeof(r));
  #else