diff --git a/src/lib.rs b/src/lib.rs
index fc43d66..adffdfd 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -123,6 +123,23 @@ pub mod buf {
 		}
 	}
 
+	impl<'a, R, T> Push<T> for &'a mut R
+	where
+		R: Push<T>,
+	{
+		fn push_checked(&mut self, item: T) -> Result<(), OutOfSpace> {
+			(**self).push_checked(item)
+		}
+
+		fn push(&mut self, item: T) {
+			(**self).push(item)
+		}
+
+		unsafe fn push_unchecked(&mut self, item: T) {
+			(**self).push(item)
+		}
+	}
+
 	pub struct OutOfSpace;
 	pub trait Push<T> {
 		fn push_checked(&mut self, item: T) -> Result<(), OutOfSpace> {
@@ -332,12 +349,13 @@ pub mod cli {
 			'b,
 			A: AsRef<str>,
 			B: From<&'b str>,
-			P: Push<ParseError>,
+			PB: Push<B>,
+			PE: Push<ParseError>,
 		>(
 			&mut self,
 			args: &'b [A],
-			mut out: Option<&mut Vec<B>>,
-			mut errors: Option<&mut P>,
+			mut out: PB,
+			mut errors: PE,
 		) {
 			let mut it = args.iter();
 			fn next_param<'a, A: AsRef<str> + 'a>(
@@ -400,24 +418,21 @@ pub mod cli {
 							},
 						}
 					} else {
-						if let Some(out) = out.as_mut() {
-							out.push(arg.as_ref().into());
-						}
+						out.push(arg.as_ref().into());
 						Ok(())
 					}
 				};
 
-				if let (Some(err), Some(errors)) = (go().err(), errors.as_mut())
-				{
+				if let Some(err) = go().err() {
 					errors.push(err);
 				}
 			}
 		}
 
-		pub fn parse_env<P: Push<ParseError>>(
+		pub fn parse_env<PS: Push<String>, PE: Push<ParseError>>(
 			&mut self,
-			out: Option<&mut Vec<String>>,
-			errors: Option<&mut P>,
+			out: PS,
+			errors: PE,
 		) {
 			let env_args = std::env::args().collect::<Vec<_>>();
 			self.parse(env_args.as_slice(), out, errors);
@@ -514,8 +529,8 @@ pub mod cli {
 			let mut errors = Buf::new(1);
 			cli.parse(
 				&["--foo", "foo", "--bar", "854", "-b", "arg"],
-				Some(&mut args),
-				Some(&mut errors),
+				&mut args,
+				&mut errors,
 			);
 			assert_eq!(foo, "foo");
 			assert_eq!(bar, 854);