diff --git a/src/lexer.rs b/src/lexer.rs
index cc762d4..e8aa1dd 100644
--- a/src/lexer.rs
+++ b/src/lexer.rs
@@ -40,7 +40,12 @@ impl<'a> Iterator for Lexer<'a> {
 impl<'a> Lexer<'a> {
     pub fn new(file: &'a Arc<File>) -> Lexer<'a> {
         Lexer {
-            buf: file.source().trim_start_matches("\u{ef}\u{bb}\u{bf}").trim_start_matches("\u{feff}").chars().peekable(),
+            buf: file
+                .source()
+                .trim_start_matches("\u{ef}\u{bb}\u{bf}")
+                .trim_start_matches("\u{feff}")
+                .chars()
+                .peekable(),
             pos: 0,
             file,
         }
diff --git a/src/parse/value/parse.rs b/src/parse/value/parse.rs
index 5577915..5effa3b 100644
--- a/src/parse/value/parse.rs
+++ b/src/parse/value/parse.rs
@@ -220,9 +220,7 @@ impl<'a> Parser<'a> {
                     .get_fn(fn_name)?
                     .ok_or(("Undefined function.", fn_name.span))?;
 
-                if !matches!(self.toks.next(), Some(Token { kind: '(', .. })) {
-                    todo!()
-                }
+                self.expect_char('(')?;
 
                 let call_args = self.parse_call_args()?;
 
diff --git a/tests/use.rs b/tests/use.rs
index 928ebec..c1017da 100644
--- a/tests/use.rs
+++ b/tests/use.rs
@@ -34,6 +34,10 @@ error!(
     unknown_function,
     "@use \"sass:math\";\na { color: math.bar(); }", "Error: Undefined function."
 );
+error!(
+    module_function_missing_open_parens,
+    "@use \"sass:math\";\na { color: math.floor; }", "Error: expected \"(\"."
+);
 test!(
     use_as,
     "@use \"sass:math\" as foo;