diff --git a/lib/parallel/processor_count.rb b/lib/parallel/processor_count.rb
index d4a045d..e06dfe5 100644
--- a/lib/parallel/processor_count.rb
+++ b/lib/parallel/processor_count.rb
@@ -12,7 +12,7 @@ def processor_count
     def physical_processor_count
       @physical_processor_count ||= begin
         ppc = case RbConfig::CONFIG["target_os"]
-        when /darwin[12]/,
+        when /darwin1/
           IO.popen("/usr/sbin/sysctl -n hw.physicalcpu").read.to_i
         when /linux/
           cores = {}  # unique physical ID / core ID combinations