diff --git a/crates/swc_css_minifier/src/compressor/rules.rs b/crates/swc_css_minifier/src/compressor/rules.rs
index e7250addbab6..900def2024f0 100644
--- a/crates/swc_css_minifier/src/compressor/rules.rs
+++ b/crates/swc_css_minifier/src/compressor/rules.rs
@@ -58,10 +58,25 @@ impl Compressor {
         }
     }
 
-    fn get_declaration_name(&self, declaration: &Declaration) -> JsWord {
-        match &declaration.name {
-            DeclarationName::Ident(Ident { value, .. }) => value.to_ascii_lowercase(),
-            DeclarationName::DashedIdent(DashedIdent { value, .. }) => value.to_ascii_lowercase(),
+    fn is_same_declaration_name(&self, left: &Declaration, right: &Declaration) -> bool {
+        match (&left.name, &right.name) {
+            (
+                DeclarationName::Ident(Ident {
+                    value: left_value, ..
+                }),
+                DeclarationName::Ident(Ident {
+                    value: right_value, ..
+                }),
+            ) => left_value.eq_ignore_ascii_case(right_value),
+            (
+                DeclarationName::DashedIdent(DashedIdent {
+                    value: left_value, ..
+                }),
+                DeclarationName::DashedIdent(DashedIdent {
+                    value: right_value, ..
+                }),
+            ) => left_value == right_value,
+            _ => false,
         }
     }
 
@@ -541,8 +556,7 @@ impl Compressor {
                 }
                 ComponentValue::Declaration(box declaration) if prev_rule.is_some() => {
                     if let Some(ComponentValue::Declaration(box prev_rule)) = &mut prev_rule {
-                        if self.get_declaration_name(prev_rule)
-                            == self.get_declaration_name(declaration)
+                        if self.is_same_declaration_name(prev_rule, declaration)
                             && prev_rule.value.eq_ignore_span(&declaration.value)
                         {
                             remove_rules_list.push(prev_index);
diff --git a/crates/swc_css_minifier/tests/fixture/compress-declaration/duplication/input.css b/crates/swc_css_minifier/tests/fixture/compress-declaration/duplication/input.css
index f3e4ba205f65..1da15d685ddc 100644
--- a/crates/swc_css_minifier/tests/fixture/compress-declaration/duplication/input.css
+++ b/crates/swc_css_minifier/tests/fixture/compress-declaration/duplication/input.css
@@ -106,3 +106,21 @@ h1{font-weight:bold}
         font-weight:bold
     }
 }
+
+:root {
+    --color: red;
+    --color: red;
+    --Color: red;
+}
+
+.class {
+    --color: red;
+    --color: red;
+    --Color: red;
+
+    .nested {
+        --color: red;
+        --color: red;
+        --Color: red;
+    }
+}
\ No newline at end of file
diff --git a/crates/swc_css_minifier/tests/fixture/compress-declaration/duplication/output.min.css b/crates/swc_css_minifier/tests/fixture/compress-declaration/duplication/output.min.css
index f845eeee6f5d..02252cdc4873 100644
--- a/crates/swc_css_minifier/tests/fixture/compress-declaration/duplication/output.min.css
+++ b/crates/swc_css_minifier/tests/fixture/compress-declaration/duplication/output.min.css
@@ -1 +1 @@
-a{color:red;.class{color:red}@media screen and (min-width:100px){color:red}@supports(display:flex){color:red;.other{color:red}}.case-insensitivity{color:red}}.font,.class,.other{>h1{font-weight:700}}.base{color:red;.class,.class-other{color:red}@media screen{.class,.class-other{color:red}}}h1{font-weight:700}.white{_color:white;color:white}h1,h2{font-weight:700}.margin{margin:10px 0}h1{font-weight:700}@media print{h1{display:block}}.other{& h1{font-weight:700}}@media print{h1,h2{font-weight:700}}
+a{color:red;.class{color:red}@media screen and (min-width:100px){color:red}@supports(display:flex){color:red;.other{color:red}}.case-insensitivity{color:red}}.font,.class,.other{>h1{font-weight:700}}.base{color:red;.class,.class-other{color:red}@media screen{.class,.class-other{color:red}}}h1{font-weight:700}.white{_color:white;color:white}h1,h2{font-weight:700}.margin{margin:10px 0}h1{font-weight:700}@media print{h1{display:block}}.other{& h1{font-weight:700}}@media print{h1,h2{font-weight:700}}:root{--color:red;--Color:red}.class{--color:red;--Color:red;.nested{--color:red;--Color:red}}