diff --git a/src/args.rs b/src/args.rs
index ef010a4..eb59663 100644
--- a/src/args.rs
+++ b/src/args.rs
@@ -77,7 +77,7 @@ pub(crate) fn eat_func_args<I: Iterator<Item = Token>>(
                         ',' => {
                             toks.next();
                             args.push(FuncArg {
-                                name,
+                                name: name.replace('_', "-"),
                                 default: Some(Value::from_tokens(
                                     &mut default.into_iter().peekable(),
                                     scope,
@@ -88,7 +88,7 @@ pub(crate) fn eat_func_args<I: Iterator<Item = Token>>(
                         }
                         ')' => {
                             args.push(FuncArg {
-                                name,
+                                name: name.replace('_', "-"),
                                 default: Some(Value::from_tokens(
                                     &mut default.into_iter().peekable(),
                                     scope,
@@ -107,7 +107,7 @@ pub(crate) fn eat_func_args<I: Iterator<Item = Token>>(
             '.' => todo!("handle varargs"),
             ')' => {
                 args.push(FuncArg {
-                    name,
+                    name: name.replace('_', "-"),
                     default: if default.is_empty() {
                         None
                     } else {
@@ -121,7 +121,7 @@ pub(crate) fn eat_func_args<I: Iterator<Item = Token>>(
                 break;
             }
             ',' => args.push(FuncArg {
-                name,
+                name: name.replace('_', "-"),
                 default: None,
             }),
             _ => {}
diff --git a/tests/mixins.rs b/tests/mixins.rs
index 6c3865d..221148f 100644
--- a/tests/mixins.rs
+++ b/tests/mixins.rs
@@ -190,7 +190,12 @@ test!(
     "a {\n  color: red;\n}\n"
 );
 test!(
-    args_interchangable_hypen_underscore,
+    args_hyphen_arg_allows_underscore,
     "@mixin foo($a-b) {\n  color: $a-b;\n  color: $a_b;\n}\na {\n  @include foo($a_b: a);\n  @include foo($a-b: a);\n}\n",
     "a {\n  color: a;\n  color: a;\n  color: a;\n  color: a;\n}\n"
 );
+test!(
+    args_underscore_arg_allows_hyphen,
+    "@mixin foo($a_b) {\n  color: $a-b;\n  color: $a_b;\n}\na {\n  @include foo($a_b: a);\n  @include foo($a-b: a);\n}\n",
+    "a {\n  color: a;\n  color: a;\n  color: a;\n  color: a;\n}\n"
+);