diff --git a/lib/monitor.rb b/lib/monitor.rb
index 044219bcbb..c4ce06794a 100644
--- a/lib/monitor.rb
+++ b/lib/monitor.rb
@@ -87,6 +87,9 @@
 # MonitorMixin module.
 #
 module MonitorMixin
+  EXCEPTION_NEVER = {Exception => :never}.freeze
+  EXCEPTION_IMMEDIATE = {Exception => :immediate}.freeze
+
   #
   # FIXME: This isn't documented in Nutshell.
   #
@@ -103,11 +106,11 @@ module MonitorMixin
     # even if no other thread doesn't signal.
     #
     def wait(timeout = nil)
-      Thread.handle_interrupt(Exception => :never) do
+      Thread.handle_interrupt(EXCEPTION_NEVER) do
         @monitor.__send__(:mon_check_owner)
         count = @monitor.__send__(:mon_exit_for_cond)
         begin
-          Thread.handle_interrupt(Exception => :immediate) do
+          Thread.handle_interrupt(EXCEPTION_IMMEDIATE) do
             @cond.wait(@monitor.instance_variable_get(:@mon_mutex), timeout)
           end
           return true
@@ -227,11 +230,11 @@ module MonitorMixin
   def mon_synchronize
     # Prevent interrupt on handling interrupts; for example timeout errors
     # it may break locking state.
-    Thread.handle_interrupt(Exception => :never){ mon_enter }
+    Thread.handle_interrupt(EXCEPTION_NEVER){ mon_enter }
     begin
       yield
     ensure
-      Thread.handle_interrupt(Exception => :never){ mon_exit }
+      Thread.handle_interrupt(EXCEPTION_NEVER){ mon_exit }
     end
   end
   alias synchronize mon_synchronize