diff --git a/src/sass/functions/macros.rs b/src/sass/functions/macros.rs
index 19cb71390..9df14b470 100644
--- a/src/sass/functions/macros.rs
+++ b/src/sass/functions/macros.rs
@@ -23,7 +23,7 @@ macro_rules! one_arg {
 
 macro_rules! def {
     ($f:expr, $name:ident( $($arg:ident$(=$val:expr)* ),* ), $body:expr) => {{
-        use crate::sass::{Functions, FormalArgs};
+        use crate::sass::functions::{Functions, FormalArgs};
         use std::sync::Arc;
         let args = FormalArgs::new(vec![ $(one_arg!($arg $(=$val)*)),* ]);
         $f.builtin_fn(name!($name), args, Arc::new($body));
@@ -31,7 +31,7 @@ macro_rules! def {
 }
 macro_rules! def_va {
     ($f:expr, $name:ident( $($arg:ident$(=$val:expr)* ),*), $body:expr) => {{
-        use crate::sass::{Functions, FormalArgs};
+        use crate::sass::functions::{Functions, FormalArgs};
         use std::sync::Arc;
         let args = FormalArgs::new_va(vec![ $(one_arg!($arg $(=$val)*)),* ]);
         $f.builtin_fn(name!($name), args, Arc::new($body));
diff --git a/src/sass/functions/mod.rs b/src/sass/functions/mod.rs
index 0bcda419e..a2528523e 100644
--- a/src/sass/functions/mod.rs
+++ b/src/sass/functions/mod.rs
@@ -89,9 +89,7 @@ impl fmt::Debug for FuncImpl {
     }
 }
 
-/// ...
-pub trait Functions {
-    /// ...
+trait Functions {
     fn builtin_fn(
         &mut self,
         name: Name,
diff --git a/src/sass/mod.rs b/src/sass/mod.rs
index c272446b0..07aacad67 100644
--- a/src/sass/mod.rs
+++ b/src/sass/mod.rs
@@ -10,7 +10,7 @@ mod value;
 
 pub use self::call_args::CallArgs;
 pub use self::formal_args::{ArgsError, FormalArgs};
-pub use self::functions::{get_global_module, Function, Functions};
+pub use self::functions::{get_global_module, Function};
 pub use self::item::{Item, UseAs};
 pub use self::mixin::Mixin;
 pub use self::name::Name;
diff --git a/tests/rust_functions.rs b/tests/rust_functions.rs
index 213f1b7ff..52b1305d3 100644
--- a/tests/rust_functions.rs
+++ b/tests/rust_functions.rs
@@ -1,5 +1,4 @@
-use lazy_static::lazy_static;
-use rsass::sass::{FormalArgs, Functions, Name};
+use rsass::sass::{Function, FormalArgs, Name};
 use rsass::value::{Number, Numeric, Rgba};
 use rsass::*;
 use std::sync::Arc;
@@ -23,42 +22,6 @@ fn simple_value() {
     );
 }
 
-#[cfg(test)]
-lazy_static! {
-    static ref TEST: Scope = {
-        fn get_number(s: &Scope, name: Name) -> Result<Numeric, Error> {
-            s.get(name.as_ref())?
-                .numeric_value()
-                .map_err(|v| Error::bad_arg(name, &v, "is not a number"))
-        }
-        let mut scope = Scope::builtin_module("test");
-        scope.builtin_fn(
-            Name::from_static("get_answer"),
-            FormalArgs::none(),
-            Arc::new(|_| Ok(css::Value::scalar(42))),
-        );
-        scope.builtin_fn(
-            Name::from_static("halfway"),
-            FormalArgs::new(vec![
-                ("a".into(), None),
-                ("b".into(), Some(sass::Value::scalar(0))),
-            ]),
-            Arc::new(|s| {
-                let a = get_number(s, "a".into())?;
-                let b = get_number(s, "b".into())?;
-                if a.unit == b.unit || b.unit.is_none() {
-                    Ok(Numeric::new(avg(a.value, b.value), a.unit).into())
-                } else if a.unit.is_none() {
-                    Ok(Numeric::new(avg(a.value, b.value), b.unit).into())
-                } else {
-                    Err(Error::S("Incopatible args".into()))
-                }
-            }),
-        );
-        scope
-    };
-}
-
 #[test]
 fn simple_function() {
     let format = output::Format {
@@ -66,8 +29,16 @@ fn simple_function() {
         precision: 5,
     };
     let scope = ScopeRef::new_global(format);
-    scope.define_module(Name::from_static("test"), ScopeRef::Builtin(&TEST));
-    let parsed = parse_scss_data(b"p { x: test.get_answer(); }").unwrap();
+    scope.define_function(
+        Name::from_static("get_answer"),
+        Function::builtin(
+            &Name::from_static(""),
+            &Name::from_static("get_answer"),
+            FormalArgs::none(),
+            Arc::new(|_| Ok(css::Value::scalar(42))),
+        ),
+    );
+    let parsed = parse_scss_data(b"p { x: get_answer(); }").unwrap();
     let file_context = FsFileContext::new();
     assert_eq!(
         String::from_utf8(
@@ -86,8 +57,35 @@ fn avg(a: Number, b: Number) -> Number {
 #[test]
 fn function_with_args() {
     let scope = ScopeRef::new_global(Default::default());
-    scope.define_module(Name::from_static("test"), ScopeRef::Builtin(&TEST));
-    let parsed = parse_scss_data(b"p { x: test.halfway(10, 18); }").unwrap();
+    scope.define_function(
+        Name::from_static("halfway"),
+        Function::builtin(
+            &Name::from_static(""),
+            &Name::from_static("halfway"),
+            FormalArgs::new(vec![
+                ("a".into(), None),
+                ("b".into(), Some(sass::Value::scalar(0))),
+            ]),
+            Arc::new(|s| {
+                let a = s
+                    .get("a")?
+                    .numeric_value()
+                    .map_err(|v| Error::bad_arg("a".into(), &v, "is not a number"))?;
+                let b = s
+                    .get("b")?
+                    .numeric_value()
+                    .map_err(|v| Error::bad_arg("b".into(), &v, "is not a number"))?;
+                if a.unit == b.unit || b.unit.is_none() {
+                    Ok(Numeric::new(avg(a.value, b.value), a.unit).into())
+                } else if a.unit.is_none() {
+                    Ok(Numeric::new(avg(a.value, b.value), b.unit).into())
+                } else {
+                    Err(Error::error("Incopatible args"))
+                }
+            }),
+        ),
+    );
+    let parsed = parse_scss_data(b"p { x: halfway(10, 18); }").unwrap();
     let format = output::Format {
         style: output::Style::Compressed,
         precision: 5,