diff --git a/src/value/parse.rs b/src/value/parse.rs
index 334b56f..d3d58ad 100644
--- a/src/value/parse.rs
+++ b/src/value/parse.rs
@@ -451,7 +451,7 @@ impl Value {
                     span,
                 }) {
                     Ok(f) => f,
-                    Err(_) => match GLOBAL_FUNCTIONS.get(&s) {
+                    Err(_) => match GLOBAL_FUNCTIONS.get(&s.replace('_', "-")) {
                         Some(f) => {
                             return Ok(IntermediateValue::Value(Spanned {
                                 node: f.0(
diff --git a/tests/color.rs b/tests/color.rs
index 157653a..8bb882a 100644
--- a/tests/color.rs
+++ b/tests/color.rs
@@ -517,11 +517,6 @@ test!(
     "a {\n  color: ie-hex-str(rgba(0, 255, 0, 0.5));\n}\n",
     "a {\n  color: #8000FF00;\n}\n"
 );
-// test!(
-//     builtin_functions_interchangable_underscore_hyphen,
-//     "a {\n  color: ie_hex-str(rgba(0, 255, 0, 0.5));\n}\n",
-//     "a {\n  color: #8000FF00;\n}\n"
-// );
 test!(
     rgba_1_arg,
     "a {\n  color: rgba(74.7% 173 93%);\n}\n",
diff --git a/tests/misc.rs b/tests/misc.rs
index 0ba0aee..38593f5 100644
--- a/tests/misc.rs
+++ b/tests/misc.rs
@@ -111,3 +111,8 @@ test!(
     "a {\n  color: foo;\n};",
     "a {\n  color: foo;\n}\n"
 );
+test!(
+    builtin_functions_interchangeable_underscore_hyphen,
+    "a {\n  color: ie_hex-str(rgba(0, 255, 0, 0.5));\n}\n",
+    "a {\n  color: #8000FF00;\n}\n"
+);