diff --git a/lib/pry/commands/watch_expression/expression.rb b/lib/pry/commands/watch_expression/expression.rb
index f9d9fa99..d01379a1 100644
--- a/lib/pry/commands/watch_expression/expression.rb
+++ b/lib/pry/commands/watch_expression/expression.rb
@@ -1,7 +1,7 @@
 class Pry
   class Command::WatchExpression
     class Expression
-      NODUP = [TrueClass, FalseClass, NilClass, Numeric].freeze
+      NODUP = [TrueClass, FalseClass, NilClass, Numeric, Symbol].freeze
       attr_reader :target, :source, :value, :previous_value
 
       def initialize(target, source)
diff --git a/lib/pry/config/behavior.rb b/lib/pry/config/behavior.rb
index d72d7afa..e4c950f0 100644
--- a/lib/pry/config/behavior.rb
+++ b/lib/pry/config/behavior.rb
@@ -1,6 +1,6 @@
 module Pry::Config::Behavior
   ASSIGNMENT = "=".freeze
-  NODUP = [TrueClass, FalseClass, NilClass, Module, Proc, Numeric].freeze
+  NODUP = [TrueClass, FalseClass, NilClass, Symbol, Numeric, Module, Proc].freeze
   RESERVED_KEYS = [
                    "[]", "[]=", "merge!",
                    "respond_to?", "key?", "refresh",