diff -Naurp a/NTS/config.m4 b/NTS/config.m4
--- a/NTS/config.m4	2020-02-11 10:37:11.093473672 +0000
+++ b/NTS/config.m4	2020-02-11 10:38:28.551693692 +0000
@@ -1060,7 +1060,6 @@ if test "$PHP_GRPC" != "no"; then
     , $ext_shared, , -fvisibility=hidden \
     -DOPENSSL_NO_ASM -D_GNU_SOURCE -DWIN32_LEAN_AND_MEAN \
     -D_HAS_EXCEPTIONS=0 -DNOMINMAX -DGRPC_ARES=0 \
-    -DGRPC_POSIX_FORK_ALLOW_PTHREAD_ATFORK=1 \
     -DGRPC_XDS_USER_AGENT_NAME_SUFFIX='"\"PHP\""' \
     -DGRPC_XDS_USER_AGENT_VERSION_SUFFIX='"\"1.42.0\""')