diff --git a/src/args.rs b/src/args.rs
index 8d8456c..8dfcc14 100644
--- a/src/args.rs
+++ b/src/args.rs
@@ -40,7 +40,7 @@ enum CallArg {
 impl CallArg {
     pub fn position(&self) -> SassResult<usize> {
         match self {
-            Self::Named(..) => todo!(),
+            Self::Named(..) => Err("found named".into()),
             Self::Positional(p) => Ok(*p),
         }
     }
@@ -58,6 +58,24 @@ impl CallArgs {
         CallArgs(HashMap::new())
     }
 
+    pub fn to_css_string(self, scope: &Scope, super_selector: &Selector) -> SassResult<String> {
+        let mut string = String::with_capacity(2 + self.len() * 10);
+        string.push('(');
+        let args = match self.get_variadic(scope, super_selector) {
+            Ok(v) => v,
+            Err(..) => return Err("Plain CSS functions don't support keyword arguments.".into()),
+        };
+        string.push_str(
+            &args
+                .iter()
+                .map(std::string::ToString::to_string)
+                .collect::<Vec<String>>()
+                .join(", "),
+        );
+        string.push(')');
+        Ok(string)
+    }
+
     /// Get argument by name
     ///
     /// Removes the argument
diff --git a/src/value/parse.rs b/src/value/parse.rs
index 355742f..61e2387 100644
--- a/src/value/parse.rs
+++ b/src/value/parse.rs
@@ -16,7 +16,7 @@ use crate::selector::Selector;
 use crate::unit::Unit;
 use crate::utils::{
     devour_whitespace, eat_comment, eat_ident, eat_ident_no_interpolation, eat_number,
-    parse_interpolation, parse_quoted_string, read_until_char, read_until_closing_paren,
+    parse_quoted_string, read_until_char, read_until_closing_paren,
     read_until_closing_square_brace, read_until_newline, IsWhitespace,
 };
 use crate::value::Value;
@@ -374,34 +374,10 @@ impl Value {
                             )?))
                         }
                         None => {
-                            s.push('(');
-                            let mut unclosed_parens = 0;
-                            while let Some(t) = toks.next() {
-                                match &t.kind {
-                                    '(' => {
-                                        unclosed_parens += 1;
-                                    }
-                                    '#' if toks.next().unwrap().kind == '{' => s.push_str(
-                                        &parse_interpolation(toks, scope, super_selector)?
-                                            .to_string(),
-                                    ),
-                                    '$' => s.push_str(
-                                        &scope
-                                            .get_var(&eat_ident(toks, scope, super_selector)?)?
-                                            .to_string(),
-                                    ),
-                                    ')' => {
-                                        if unclosed_parens <= 1 {
-                                            s.push(')');
-                                            break;
-                                        } else {
-                                            unclosed_parens -= 1;
-                                        }
-                                    }
-                                    _ => {}
-                                }
-                                s.push_str(&t.kind.to_string());
-                            }
+                            s.push_str(
+                                &eat_call_args(toks, scope, super_selector)?
+                                    .to_css_string(scope, super_selector)?,
+                            );
                             return Ok(IntermediateValue::Value(Value::Ident(s, QuoteKind::None)));
                         }
                     },
diff --git a/tests/plain-css-fn.rs b/tests/plain-css-fn.rs
new file mode 100644
index 0000000..9a8d27a
--- /dev/null
+++ b/tests/plain-css-fn.rs
@@ -0,0 +1,45 @@
+#![cfg(test)]
+
+#[macro_use]
+mod macros;
+
+test!(
+    type_is_string,
+    "a {\n  color: type-of(foo(1+1));\n}\n",
+    "a {\n  color: string;\n}\n"
+);
+test!(
+    evaluates_arguments,
+    "a {\n  color: foo(1+1);\n}\n",
+    "a {\n  color: foo(2);\n}\n"
+);
+test!(
+    arguments_are_comma_separated,
+    "a {\n  color: foo(1+1, 2+3, 4+5);\n}\n",
+    "a {\n  color: foo(2, 5, 9);\n}\n"
+);
+test!(
+    converts_sql_quotes,
+    "a {\n  color: foo('hi');\n}\n",
+    "a {\n  color: foo(\"hi\");\n}\n"
+);
+test!(
+    super_selector,
+    "a {\n  color: foo(&);\n}\n",
+    "a {\n  color: foo(a);\n}\n"
+);
+test!(
+    nested_plain_css_fn,
+    "a {\n  color: foo(foo(foo(foo(1+1))));\n}\n",
+    "a {\n  color: foo(foo(foo(foo(2))));\n}\n"
+);
+error!(
+    disallows_named_arguments,
+    "a {\n  color: foo($a: 1+1);\n}\n",
+    "Error: Plain CSS functions don't support keyword arguments."
+);
+test!(
+    evalutes_variables,
+    "a {\n  $primary: #f2ece4;\n  $accent: #e1d7d2;\n  color: radial-gradient($primary, $accent);\n}\n",
+    "a {\n  color: radial-gradient(#f2ece4, #e1d7d2);\n}\n"
+);