diff --git a/src/builtin/color/rgb.rs b/src/builtin/color/rgb.rs
index 350795b..8f8c5a1 100644
--- a/src/builtin/color/rgb.rs
+++ b/src/builtin/color/rgb.rs
@@ -39,7 +39,7 @@ fn inner_rgb(
                 .into());
         }
 
-        let blue = match channels.pop() {
+        let blue = match channels.pop().map(|v| v.eval(args.span()).unwrap().node) {
             Some(Value::Dimension(n, Unit::None)) => n,
             Some(Value::Dimension(n, Unit::Percent)) => (n / Number::from(100)) * Number::from(255),
             Some(v) if v.is_special_function() => {
@@ -66,7 +66,7 @@ fn inner_rgb(
             None => return Err(("Missing element $blue.", args.span()).into()),
         };
 
-        let green = match channels.pop() {
+        let green = match channels.pop().map(|v| v.eval(args.span()).unwrap().node) {
             Some(Value::Dimension(n, Unit::None)) => n,
             Some(Value::Dimension(n, Unit::Percent)) => (n / Number::from(100)) * Number::from(255),
             Some(v) if v.is_special_function() => {
@@ -92,7 +92,7 @@ fn inner_rgb(
             None => return Err(("Missing element $green.", args.span()).into()),
         };
 
-        let red = match channels.pop() {
+        let red = match channels.pop().map(|v| v.eval(args.span()).unwrap().node) {
             Some(Value::Dimension(n, Unit::None)) => n,
             Some(Value::Dimension(n, Unit::Percent)) => (n / Number::from(100)) * Number::from(255),
             Some(v) if v.is_special_function() => {
diff --git a/tests/color.rs b/tests/color.rs
index 8bd523e..4443206 100644
--- a/tests/color.rs
+++ b/tests/color.rs
@@ -572,3 +572,8 @@ test!(
     "a {\n  color: opacity(transparent);\n}\n",
     "a {\n  color: 0;\n}\n"
 );
+test!(
+    negative_values_in_rgb,
+    "a {\n  color: rgb(-1 -1 -1);\n}\n",
+    "a {\n  color: black;\n}\n"
+);