diff --git a/src/app.rs b/src/app.rs
index 8b7c281..6a25521 100644
--- a/src/app.rs
+++ b/src/app.rs
@@ -160,10 +160,13 @@ pub fn app() {
     die!("Justfile contains no recipes");
   };
 
-  let dry_run = matches.is_present("dry-run");
-  let evaluate = matches.is_present("evaluate");
+  let options = super::RunOptions {
+    dry_run:   matches.is_present("dry-run"),
+    evaluate:  matches.is_present("evaluate"),
+    overrides: overrides,
+  };
 
-  if let Err(run_error) = justfile.run(&overrides, &arguments, dry_run, evaluate) {
+  if let Err(run_error) = justfile.run(&arguments, &options) {
     warn!("{}", run_error);
     match run_error {
       RunError::Code{code, .. } | RunError::BacktickCode{code, ..} => process::exit(code),
diff --git a/src/lib.rs b/src/lib.rs
index 58f710b..497c455 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -832,6 +832,13 @@ struct Justfile<'a> {
   exports:     Set<&'a str>,
 }
 
+#[derive(Default)]
+struct RunOptions<'a> {
+  dry_run:   bool,
+  evaluate:  bool,
+  overrides: Map<&'a str, &'a str>,
+}
+
 impl<'a, 'b> Justfile<'a> where 'a: 'b {
   fn first(&self) -> Option<&'a str> {
     let mut first: Option<&Recipe<'a>> = None;
@@ -857,12 +864,10 @@ impl<'a, 'b> Justfile<'a> where 'a: 'b {
 
   fn run(
     &'a self,
-    overrides: &Map<&'a str, &'a str>,
     arguments: &[&'a str],
-    dry_run:   bool,
-    evaluate:  bool,
+    options: &RunOptions<'a>,
   ) -> Result<(), RunError<'a>> {
-    let unknown_overrides = overrides.keys().cloned()
+    let unknown_overrides = options.overrides.keys().cloned()
       .filter(|name| !self.assignments.contains_key(name))
       .collect::<Vec<_>>();
 
@@ -870,8 +875,8 @@ impl<'a, 'b> Justfile<'a> where 'a: 'b {
       return Err(RunError::UnknownOverrides{overrides: unknown_overrides});
     }
 
-    let scope = try!(evaluate_assignments(&self.assignments, overrides));
-    if evaluate {
+    let scope = try!(evaluate_assignments(&self.assignments, &options.overrides));
+    if options.evaluate {
       for (name, value) in scope {
         println!("{} = \"{}\"", name, value);
       }
@@ -894,7 +899,7 @@ impl<'a, 'b> Justfile<'a> where 'a: 'b {
               expected: recipe.parameters.len(),
             });
           }
-          try!(self.run_recipe(recipe, rest, &scope, &mut ran, dry_run));
+          try!(self.run_recipe(recipe, rest, &scope, &mut ran, options.dry_run));
           return Ok(());
         }
       } else {
@@ -912,7 +917,7 @@ impl<'a, 'b> Justfile<'a> where 'a: 'b {
       return Err(RunError::UnknownRecipes{recipes: missing});
     }
     for recipe in arguments.iter().map(|name| &self.recipes[name]) {
-      try!(self.run_recipe(recipe, &[], &scope, &mut ran, dry_run));
+      try!(self.run_recipe(recipe, &[], &scope, &mut ran, options.dry_run));
     }
     Ok(())
   }
diff --git a/src/unit.rs b/src/unit.rs
index 9313e82..e88663d 100644
--- a/src/unit.rs
+++ b/src/unit.rs
@@ -1,9 +1,8 @@
 extern crate tempdir;
 extern crate brev;
 
-use super::{Token, Error, ErrorKind, Justfile, RunError};
+use super::{Token, Error, ErrorKind, Justfile, RunError, RunOptions};
 use super::TokenKind::*;
-use std::collections::BTreeMap as Map;
 
 fn tokenize_success(text: &str, expected_summary: &str) {
   let tokens = super::tokenize(text).unwrap();
@@ -617,7 +616,7 @@ fn conjoin_and() {
 
 #[test]
 fn unknown_recipes() {
-  match parse_success("a:\nb:\nc:").run(&Map::new(), &["a", "x", "y", "z"], false, false).unwrap_err() {
+  match parse_success("a:\nb:\nc:").run(&["a", "x", "y", "z"], &Default::default()).unwrap_err() {
     RunError::UnknownRecipes{recipes} => assert_eq!(recipes, &["x", "y", "z"]),
     other => panic!("expected an unknown recipe error, but got: {}", other),
   }
@@ -742,7 +741,7 @@ a:
       x
 ";
 
-  match parse_success(text).run(&Map::new(), &["a"], false, false).unwrap_err() {
+  match parse_success(text).run(&["a"], &Default::default()).unwrap_err() {
     RunError::Code{recipe, code} => {
       assert_eq!(recipe, "a");
       assert_eq!(code, 200);
@@ -753,7 +752,8 @@ a:
 
 #[test]
 fn code_error() {
-  match parse_success("fail:\n @function x { return 100; }; x").run(&Map::new(), &["fail"], false, false).unwrap_err() {
+  match parse_success("fail:\n @function x { return 100; }; x")
+    .run(&["fail"], &Default::default()).unwrap_err() {
     RunError::Code{recipe, code} => {
       assert_eq!(recipe, "fail");
       assert_eq!(code, 100);
@@ -768,7 +768,7 @@ fn run_args() {
 a return code:
  @function x { {{return}} {{code + "0"}}; }; x"#;
 
-  match parse_success(text).run(&Map::new(), &["a", "return", "15"], false, false).unwrap_err() {
+  match parse_success(text).run(&["a", "return", "15"], &Default::default()).unwrap_err() {
     RunError::Code{recipe, code} => {
       assert_eq!(recipe, "a");
       assert_eq!(code, 150);
@@ -779,7 +779,7 @@ a return code:
 
 #[test]
 fn missing_args() {
-  match parse_success("a b c d:").run(&Map::new(), &["a", "b", "c"], false, false).unwrap_err() {
+  match parse_success("a b c d:").run(&["a", "b", "c"], &Default::default()).unwrap_err() {
     RunError::ArgumentCountMismatch{recipe, found, expected} => {
       assert_eq!(recipe, "a");
       assert_eq!(found, 2);
@@ -791,7 +791,8 @@ fn missing_args() {
 
 #[test]
 fn missing_default() {
-  match parse_success("a b c d:\n echo {{b}}{{c}}{{d}}").run(&Map::new(), &["a"], false, false).unwrap_err() {
+  match parse_success("a b c d:\n echo {{b}}{{c}}{{d}}")
+        .run(&["a"], &Default::default()).unwrap_err() {
     RunError::ArgumentCountMismatch{recipe, found, expected} => {
       assert_eq!(recipe, "a");
       assert_eq!(found, 0);
@@ -803,7 +804,8 @@ fn missing_default() {
 
 #[test]
 fn backtick_code() {
-  match parse_success("a:\n echo {{`function f { return 100; }; f`}}").run(&Map::new(), &["a"], false, false).unwrap_err() {
+  match parse_success("a:\n echo {{`function f { return 100; }; f`}}")
+        .run(&["a"], &Default::default()).unwrap_err() {
     RunError::BacktickCode{code, token} => {
       assert_eq!(code, 100);
       assert_eq!(token.lexeme, "`function f { return 100; }; f`");
@@ -814,11 +816,11 @@ fn backtick_code() {
 
 #[test]
 fn unknown_overrides() {
-  let mut overrides = Map::new();
-  overrides.insert("foo", "bar");
-  overrides.insert("baz", "bob");
+  let mut options: RunOptions = Default::default();
+  options.overrides.insert("foo", "bar");
+  options.overrides.insert("baz", "bob");
   match parse_success("a:\n echo {{`function f { return 100; }; f`}}")
-  .run(&overrides, &["a"], false, false).unwrap_err() {
+  .run(&["a"], &options).unwrap_err() {
     RunError::UnknownOverrides{overrides} => {
       assert_eq!(overrides, &["baz", "foo"]);
     },