diff --git a/core/thread/thread_variable_get_spec.rb b/core/thread/thread_variable_get_spec.rb
index 0ad19bfd8..67017771f 100644
--- a/core/thread/thread_variable_get_spec.rb
+++ b/core/thread/thread_variable_get_spec.rb
@@ -14,12 +14,40 @@
   end
 
   it "returns the value previously set by #thread_variable_set" do
-    @t.thread_variable_set :a, 49
+    @t.thread_variable_set(:a, 49)
     @t.thread_variable_get(:a).should == 49
   end
 
   it "returns a value private to self" do
-    @t.thread_variable_set :thread_variable_get_spec, 82
+    @t.thread_variable_set(:thread_variable_get_spec, 82)
     Thread.current.thread_variable_get(:thread_variable_get_spec).should be_nil
   end
+
+  it "accepts String and Symbol keys interchangeably" do
+    @t.thread_variable_set("a", 49)
+    @t.thread_variable_get("a").should == 49
+    @t.thread_variable_get(:a).should == 49
+  end
+
+  it "converts a key that is neither String nor Symbol with #to_str" do
+    key = mock('key')
+    key.should_receive(:to_str).and_return('a')
+    @t.thread_variable_set(:a, 49)
+    @t.thread_variable_get(key).should == 49
+  end
+
+  it "does not raise FrozenError if the thread is frozen" do
+    @t.freeze
+    @t.thread_variable_get(:a).should be_nil
+  end
+
+  it "does not raise a TypeError if the key is neither Symbol nor String, nor responds to #to_str" do
+    @t.thread_variable_get(123).should be_nil
+  end
+
+  it "does not try to convert the key with #to_sym" do
+    key = mock('key')
+    key.should_not_receive(:to_sym)
+    @t.thread_variable_get(key).should be_nil
+  end
 end
diff --git a/core/thread/thread_variable_set_spec.rb b/core/thread/thread_variable_set_spec.rb
index 1338c306c..c262a6614 100644
--- a/core/thread/thread_variable_set_spec.rb
+++ b/core/thread/thread_variable_set_spec.rb
@@ -10,17 +10,53 @@
   end
 
   it "returns the value set" do
-    (@t.thread_variable_set :a, 2).should == 2
+    @t.thread_variable_set(:a, 2).should == 2
   end
 
   it "sets a value that will be returned by #thread_variable_get" do
-    @t.thread_variable_set :a, 49
+    @t.thread_variable_set(:a, 49)
     @t.thread_variable_get(:a).should == 49
   end
 
   it "sets a value private to self" do
-    @t.thread_variable_set :thread_variable_get_spec, 82
+    @t.thread_variable_set(:thread_variable_get_spec, 82)
     @t.thread_variable_get(:thread_variable_get_spec).should == 82
     Thread.current.thread_variable_get(:thread_variable_get_spec).should be_nil
   end
+
+  it "accepts String and Symbol keys interchangeably" do
+    @t.thread_variable_set('a', 49)
+    @t.thread_variable_get('a').should == 49
+
+    @t.thread_variable_set(:a, 50)
+    @t.thread_variable_get('a').should == 50
+  end
+
+  it "converts a key that is neither String nor Symbol with #to_str" do
+    key = mock('key')
+    key.should_receive(:to_str).and_return('a')
+    @t.thread_variable_set(key, 49)
+    @t.thread_variable_get(:a).should == 49
+  end
+
+  it "removes a key if the value is nil" do
+    @t.thread_variable_set(:a, 52)
+    @t.thread_variable_set(:a, nil)
+    @t.thread_variable?(:a).should be_false
+  end
+
+  it "raises a FrozenError if the thread is frozen" do
+    @t.freeze
+    -> { @t.thread_variable_set(:a, 1) }.should raise_error(FrozenError, "can't modify frozen thread locals")
+  end
+
+  it "raises a TypeError if the key is neither Symbol nor String, nor responds to #to_str" do
+    -> { @t.thread_variable_set(123, 1) }.should raise_error(TypeError, '123 is not a symbol')
+  end
+
+  it "does not try to convert the key with #to_sym" do
+    key = mock('key')
+    key.should_not_receive(:to_sym)
+    -> { @t.thread_variable_set(key, 42) }.should raise_error(TypeError, "#{key.inspect} is not a symbol")
+  end
 end
diff --git a/core/thread/thread_variable_spec.rb b/core/thread/thread_variable_spec.rb
index 6bd1950c0..d64e6ec63 100644
--- a/core/thread/thread_variable_spec.rb
+++ b/core/thread/thread_variable_spec.rb
@@ -10,12 +10,44 @@
   end
 
   it "returns false if the thread variables do not contain 'key'" do
-    @t.thread_variable_set :a, 2
+    @t.thread_variable_set(:a, 2)
     @t.thread_variable?(:b).should be_false
   end
 
   it "returns true if the thread variables contain 'key'" do
-    @t.thread_variable_set :a, 2
+    @t.thread_variable_set(:a, 2)
     @t.thread_variable?(:a).should be_true
   end
+
+  it "accepts String and Symbol keys interchangeably" do
+    @t.thread_variable?('a').should be_false
+    @t.thread_variable?(:a).should be_false
+
+    @t.thread_variable_set(:a, 49)
+
+    @t.thread_variable?('a').should be_true
+    @t.thread_variable?(:a).should be_true
+  end
+
+  it "converts a key that is neither String nor Symbol with #to_str" do
+    key = mock('key')
+    key.should_receive(:to_str).and_return('a')
+    @t.thread_variable_set(:a, 49)
+    @t.thread_variable?(key).should be_true
+  end
+
+  it "does not raise FrozenError if the thread is frozen" do
+    @t.freeze
+    @t.thread_variable?(:a).should be_false
+  end
+
+  it "does not raise a TypeError if the key is neither Symbol nor String, nor responds to #to_str" do
+    @t.thread_variable?(123).should be_false
+  end
+
+  it "does not try to convert the key with #to_sym" do
+    key = mock('key')
+    key.should_not_receive(:to_sym)
+    @t.thread_variable?(key).should be_false
+  end
 end
diff --git a/core/thread/thread_variables_spec.rb b/core/thread/thread_variables_spec.rb
index 1bd68b17f..51ceef337 100644
--- a/core/thread/thread_variables_spec.rb
+++ b/core/thread/thread_variables_spec.rb
@@ -10,15 +10,15 @@
   end
 
   it "returns the keys of all the values set" do
-    @t.thread_variable_set :a, 2
-    @t.thread_variable_set :b, 4
-    @t.thread_variable_set :c, 6
+    @t.thread_variable_set(:a, 2)
+    @t.thread_variable_set(:b, 4)
+    @t.thread_variable_set(:c, 6)
     @t.thread_variables.sort.should == [:a, :b, :c]
   end
 
-  it "sets a value private to self" do
-    @t.thread_variable_set :a, 82
-    @t.thread_variable_set :b, 82
+  it "returns the keys private to self" do
+    @t.thread_variable_set(:a, 82)
+    @t.thread_variable_set(:b, 82)
     Thread.current.thread_variables.should_not include(:a, :b)
   end
 
@@ -26,4 +26,14 @@
     Thread.current.thread_variables.should == []
     @t.thread_variables.should == []
   end
+
+  it "returns keys as Symbols" do
+    key = mock('key')
+    key.should_receive(:to_str).and_return('a')
+
+    @t.thread_variable_set(key, 49)
+    @t.thread_variable_set('b', 50)
+    @t.thread_variable_set(:c, 51)
+    @t.thread_variables.sort.should == [:a, :b, :c]
+  end
 end