diff --git a/ruby/ext/google/protobuf_c/extconf.rb b/ruby/ext/google/protobuf_c/extconf.rb
index f97b9b5b25..5a63119e02 100755
--- a/ruby/ext/google/protobuf_c/extconf.rb
+++ b/ruby/ext/google/protobuf_c/extconf.rb
@@ -22,7 +22,12 @@ debug_enabled = ENV["PROTOBUF_CONFIG"] == "dbg"
 
 additional_c_flags = debug_enabled ? "-O0 -fno-omit-frame-pointer -fvisibility=default -g" : "-O3 -DNDEBUG -fvisibility=hidden"
 
-if RUBY_PLATFORM =~ /darwin/ || RUBY_PLATFORM =~ /linux/ || RUBY_PLATFORM =~ /freebsd/
+if RUBY_PLATFORM =~ /mswin/
+  # cl.exe does not understand GCC-style flags. C11 or later is required
+  # for _Generic, which the upb MSVC atomics fall back on. c17 is the
+  # highest C standard mode cl.exe supports.
+  $CFLAGS += debug_enabled ? " -std:c17 -Od" : " -std:c17 -DNDEBUG"
+elsif RUBY_PLATFORM =~ /darwin/ || RUBY_PLATFORM =~ /linux/ || RUBY_PLATFORM =~ /freebsd/
   $CFLAGS += " -std=gnu99 -Wall -Wsign-compare -Wno-declaration-after-statement #{additional_c_flags}"
 else
   $CFLAGS += " -std=gnu99 #{additional_c_flags}"
diff --git a/ruby/ext/google/protobuf_c/protobuf.c b/ruby/ext/google/protobuf_c/protobuf.c
index aff8fab38a..5c8f046d3c 100644
--- a/ruby/ext/google/protobuf_c/protobuf.c
+++ b/ruby/ext/google/protobuf_c/protobuf.c
@@ -379,7 +379,7 @@ static VALUE Google_Protobuf_Internal_allocation_count_fail_on(VALUE self,
 
 // This must be named "Init_protobuf_c" because the Ruby module is named
 // "protobuf_c" -- the VM looks for this symbol in our .so.
-__attribute__((visibility("default"))) void Init_protobuf_c() {
+RUBY_FUNC_EXPORTED void Init_protobuf_c() {
   VALUE google = rb_define_module("Google");
   VALUE protobuf = rb_define_module_under(google, "Protobuf");