diff --git a/hash.c b/hash.c
index e9d994bf70..191bbe4955 100644
--- a/hash.c
+++ b/hash.c
@@ -4766,12 +4766,21 @@ env_delete(VALUE name)
 
 /*
  * call-seq:
- *   ENV.delete(name)                  -> value
- *   ENV.delete(name) { |name| block } -> value
- *
- * Deletes the environment variable with +name+ and returns the value of the
- * variable.  If a block is given it will be called when the named environment
- * does not exist.
+ *   ENV.delete(name)                          -> value
+ *   ENV.delete(name) { |name| block }         -> value
+ *   ENV.delete(missing_name)                  -> nil
+ *   ENV.delete(missing_name) { |name| block } -> nil
+ *
+ * Deletes the environment variable for +name+ if it exists (ignoring the block, if given); returns +nil+:
+ *   ENV.delete('LINES') # => '300'
+ *   ENV.delete('COLUMNS') { |name| fail 'boo' } # => '120'
+ * Returns +nil+ if the environment variable does not exist and block not given:
+ *   ENV.delete('NOSUCH') # => nil
+ * Calls the block and returns +nil+ if the environment variable does not exist and block given:
+ *   ENV.delete('NOSUCH') { |name| } # => nil
+ *
+ * Raises TypeError if +name+ is not a +String+:
+ *   ENV.delete(1) # => TypeError raised
  */
 static VALUE
 env_delete_m(VALUE obj, VALUE name)
diff --git a/spec/ruby/core/env/delete_spec.rb b/spec/ruby/core/env/delete_spec.rb
index 1e677fb252..eb85d26918 100644
--- a/spec/ruby/core/env/delete_spec.rb
+++ b/spec/ruby/core/env/delete_spec.rb
@@ -16,9 +16,25 @@
     ENV.delete("foo").should == "bar"
   end
 
+  it "ignores the block if the environment variable exists" do
+    ENV["foo"] = "bar"
+    begin
+      -> { ENV.delete("foo") { |name| fail name } }.should_not raise_error(RuntimeError)
+    end
+  end
+
   it "yields the name to the given block if the named environment variable does not exist" do
     ENV.delete("foo")
     ENV.delete("foo") { |name| ScratchPad.record name }
     ScratchPad.recorded.should == "foo"
   end
+
+  it "returns nil if the named environment variable does not exist and block given" do
+    ENV.delete("foo")
+    ENV.delete("foo") { |name| name }.should == nil
+  end
+
+  it "raises TypeError if name is not a String" do
+    -> { ENV.delete(1) }.should raise_error(TypeError)
+  end
 end