diff --git a/tool/search-cgvars.rb b/tool/search-cgvars.rb
index b368749910..c62641a3ff 100644
--- a/tool/search-cgvars.rb
+++ b/tool/search-cgvars.rb
@@ -1,11 +1,16 @@
 #
-# Listing C's global variables in .so or .o using "objdump -t" (elf64-x86-64)
+# Listing C's global variables in .so or .o, or .bundle on Mac OS using "objdump -t" (elf64-x86-64)
 # to check ractor-safety.
 #
-# Usage: ruby search-cgvars.rb foo.so bar.o
+# Usage: ruby search-cgvars.rb foo.so bar.o .ext/x86_64-darwin18/psych.bundle
 #
+MAC_OS = RbConfig::CONFIG['host_os'].match? /darwin|mac os/
+
 def gvars file
   # '0000000000031ac8 g     O .bss   0000000000000008              rb_cSockIfaddr'
+  # On mac, with .bundle files:
+  # '0000000000004258 l     O __DATA,__bss  _passwd_blocking'
+
   strs = `objdump -t #{file}`
   found = {}
   strs.each_line{|line|
@@ -13,10 +18,14 @@ def gvars file
       addr = line[0...16]
       flags = line[17...24].tr(' ', '').split(//).sort.uniq
       rest = line[25..]
-      seg, size, name = rest.split(/\s+/)
+      if MAC_OS
+        seg, name = rest.split(/\s+/)
+      else
+        seg, size, name = rest.split(/\s+/)
+      end
       if flags.include?('O')
         # p [addr, flags, seg, size, name]
-        found[name] = [flags, seg, size]
+        found[name] = [flags, seg, *size]
       end
     end
   }
@@ -25,14 +34,18 @@ def gvars file
     [flags, name]
   }.each{|name, rest|
     flags, seg, size = *rest
-    next if size.to_i == 0 && seg != '*UND*'
+    next if (size.to_i == 0 && !MAC_OS) && seg != '*UND*'
     case seg
     when ".rodata", ".data.rel.ro", ".got.plt", ".eh_frame", ".fini_array"
       next
+    when /,__const$/ # Mac OS
+      next
     end
     case name
     when /^id_/, /^rbimpl_id/, /^sym_/, /^rb_[cme]/, /\Acompleted\.\d+\z/
       next
+    when /^_id_/, /\.rbimpl_id(\.\d+)?$/ # Mac OS
+      next
     end
     puts "  %40s %s" % [name, rest.inspect]
   }