diff --git a/plugin-packs/postcss-preset-env/test/basic.autoprefixer.expect.css b/plugin-packs/postcss-preset-env/test/basic.autoprefixer.expect.css
index 9eec82e57..1995ca4f6 100644
--- a/plugin-packs/postcss-preset-env/test/basic.autoprefixer.expect.css
+++ b/plugin-packs/postcss-preset-env/test/basic.autoprefixer.expect.css
@@ -611,3 +611,21 @@
 	text-decoration: overline wavy pink;
 	text-decoration-thickness: 3px;
 }
+
+[dir="ltr"] .stage__container {
+	left: 1rem;
+	left: var(--size, 1rem);
+}
+
+[dir="rtl"] .stage__container {
+	right: 1rem;
+	right: var(--size, 1rem);
+}
+
+[dir="ltr"] .stage__container {
+	left: 1rem;
+}
+
+[dir="rtl"] .stage__container {
+	right: 1rem;
+}
diff --git a/plugin-packs/postcss-preset-env/test/basic.autoprefixer.false.expect.css b/plugin-packs/postcss-preset-env/test/basic.autoprefixer.false.expect.css
index 9eec82e57..1995ca4f6 100644
--- a/plugin-packs/postcss-preset-env/test/basic.autoprefixer.false.expect.css
+++ b/plugin-packs/postcss-preset-env/test/basic.autoprefixer.false.expect.css
@@ -611,3 +611,21 @@
 	text-decoration: overline wavy pink;
 	text-decoration-thickness: 3px;
 }
+
+[dir="ltr"] .stage__container {
+	left: 1rem;
+	left: var(--size, 1rem);
+}
+
+[dir="rtl"] .stage__container {
+	right: 1rem;
+	right: var(--size, 1rem);
+}
+
+[dir="ltr"] .stage__container {
+	left: 1rem;
+}
+
+[dir="rtl"] .stage__container {
+	right: 1rem;
+}
diff --git a/plugin-packs/postcss-preset-env/test/basic.ch38.expect.css b/plugin-packs/postcss-preset-env/test/basic.ch38.expect.css
index 014f3e4e4..33defb847 100644
--- a/plugin-packs/postcss-preset-env/test/basic.ch38.expect.css
+++ b/plugin-packs/postcss-preset-env/test/basic.ch38.expect.css
@@ -523,3 +523,21 @@
 	        text-decoration: overline wavy pink;
 	text-decoration-thickness: 3px;
 }
+
+[dir="ltr"] .stage__container {
+	left: 1rem;
+	left: var(--size, 1rem);
+}
+
+[dir="rtl"] .stage__container {
+	right: 1rem;
+	right: var(--size, 1rem);
+}
+
+[dir="ltr"] .stage__container {
+	left: 1rem;
+}
+
+[dir="rtl"] .stage__container {
+	right: 1rem;
+}
diff --git a/plugin-packs/postcss-preset-env/test/basic.ch88-ff78-saf10.expect.css b/plugin-packs/postcss-preset-env/test/basic.ch88-ff78-saf10.expect.css
index 2238511ea..924a548d0 100644
--- a/plugin-packs/postcss-preset-env/test/basic.ch88-ff78-saf10.expect.css
+++ b/plugin-packs/postcss-preset-env/test/basic.ch88-ff78-saf10.expect.css
@@ -525,3 +525,11 @@ h1.test-custom-selectors,h2.test-custom-selectors,h3.test-custom-selectors,h4.te
 	        text-decoration: overline wavy pink;
 	text-decoration-thickness: 3px;
 }
+
+[dir="ltr"] .stage__container {
+	left: var(--size, 1rem);
+}
+
+[dir="rtl"] .stage__container {
+	right: var(--size, 1rem);
+}
diff --git a/plugin-packs/postcss-preset-env/test/basic.ch88-ff78.expect.css b/plugin-packs/postcss-preset-env/test/basic.ch88-ff78.expect.css
index 21442ccca..86f44efcc 100644
--- a/plugin-packs/postcss-preset-env/test/basic.ch88-ff78.expect.css
+++ b/plugin-packs/postcss-preset-env/test/basic.ch88-ff78.expect.css
@@ -507,3 +507,11 @@ h1.test-custom-selectors,h2.test-custom-selectors,h3.test-custom-selectors,h4.te
 .text-decoration-shorthand {
 	text-decoration: 3px wavy pink overline;
 }
+
+[dir="ltr"] .stage__container {
+	left: var(--size, 1rem);
+}
+
+[dir="rtl"] .stage__container {
+	right: var(--size, 1rem);
+}
diff --git a/plugin-packs/postcss-preset-env/test/basic.ch88-ff78.no-is-pseudo.expect.css b/plugin-packs/postcss-preset-env/test/basic.ch88-ff78.no-is-pseudo.expect.css
index 21442ccca..86f44efcc 100644
--- a/plugin-packs/postcss-preset-env/test/basic.ch88-ff78.no-is-pseudo.expect.css
+++ b/plugin-packs/postcss-preset-env/test/basic.ch88-ff78.no-is-pseudo.expect.css
@@ -507,3 +507,11 @@ h1.test-custom-selectors,h2.test-custom-selectors,h3.test-custom-selectors,h4.te
 .text-decoration-shorthand {
 	text-decoration: 3px wavy pink overline;
 }
+
+[dir="ltr"] .stage__container {
+	left: var(--size, 1rem);
+}
+
+[dir="rtl"] .stage__container {
+	right: var(--size, 1rem);
+}
diff --git a/plugin-packs/postcss-preset-env/test/basic.css b/plugin-packs/postcss-preset-env/test/basic.css
index 260b431ce..5aed08f5d 100644
--- a/plugin-packs/postcss-preset-env/test/basic.css
+++ b/plugin-packs/postcss-preset-env/test/basic.css
@@ -405,3 +405,7 @@
 .text-decoration-shorthand {
 	text-decoration: 3px wavy pink overline;
 }
+
+.stage__container {
+	inset-inline-start: var(--size, 1rem);
+}
diff --git a/plugin-packs/postcss-preset-env/test/basic.expect.css b/plugin-packs/postcss-preset-env/test/basic.expect.css
index 1dd2ea5c1..5f2af0aff 100644
--- a/plugin-packs/postcss-preset-env/test/basic.expect.css
+++ b/plugin-packs/postcss-preset-env/test/basic.expect.css
@@ -635,3 +635,21 @@
 	        text-decoration: overline wavy pink;
 	text-decoration-thickness: 3px;
 }
+
+[dir="ltr"] .stage__container {
+	left: 1rem;
+	left: var(--size, 1rem);
+}
+
+[dir="rtl"] .stage__container {
+	right: 1rem;
+	right: var(--size, 1rem);
+}
+
+[dir="ltr"] .stage__container {
+	left: 1rem;
+}
+
+[dir="rtl"] .stage__container {
+	right: 1rem;
+}
diff --git a/plugin-packs/postcss-preset-env/test/basic.ff49.expect.css b/plugin-packs/postcss-preset-env/test/basic.ff49.expect.css
index aa7003b4a..baa693851 100644
--- a/plugin-packs/postcss-preset-env/test/basic.ff49.expect.css
+++ b/plugin-packs/postcss-preset-env/test/basic.ff49.expect.css
@@ -524,3 +524,11 @@
 	text-decoration: overline wavy pink;
 	text-decoration-thickness: 3px;
 }
+
+.stage__container:dir(ltr) {
+	left: var(--size, 1rem);
+}
+
+.stage__container:dir(rtl) {
+	right: var(--size, 1rem);
+}
diff --git a/plugin-packs/postcss-preset-env/test/basic.ff66.expect.css b/plugin-packs/postcss-preset-env/test/basic.ff66.expect.css
index 466208c71..3182e8270 100644
--- a/plugin-packs/postcss-preset-env/test/basic.ff66.expect.css
+++ b/plugin-packs/postcss-preset-env/test/basic.ff66.expect.css
@@ -505,3 +505,7 @@
 	text-decoration: overline wavy pink;
 	text-decoration-thickness: 3px;
 }
+
+.stage__container {
+	inset-inline-start: var(--size, 1rem);
+}
diff --git a/plugin-packs/postcss-preset-env/test/basic.ie10.expect.css b/plugin-packs/postcss-preset-env/test/basic.ie10.expect.css
index 202d5ba73..1285c6f63 100644
--- a/plugin-packs/postcss-preset-env/test/basic.ie10.expect.css
+++ b/plugin-packs/postcss-preset-env/test/basic.ie10.expect.css
@@ -652,3 +652,21 @@
 	text-decoration: overline wavy pink;
 	text-decoration-thickness: 3px;
 }
+
+[dir="ltr"] .stage__container {
+	left: 1rem;
+	left: var(--size, 1rem);
+}
+
+[dir="rtl"] .stage__container {
+	right: 1rem;
+	right: var(--size, 1rem);
+}
+
+[dir="ltr"] .stage__container {
+	left: 1rem;
+}
+
+[dir="rtl"] .stage__container {
+	right: 1rem;
+}
diff --git a/plugin-packs/postcss-preset-env/test/basic.nesting.false.expect.css b/plugin-packs/postcss-preset-env/test/basic.nesting.false.expect.css
index 2d2d97020..7a23e5c22 100644
--- a/plugin-packs/postcss-preset-env/test/basic.nesting.false.expect.css
+++ b/plugin-packs/postcss-preset-env/test/basic.nesting.false.expect.css
@@ -631,3 +631,21 @@ h1.test-custom-selectors,h2.test-custom-selectors,h3.test-custom-selectors,h4.te
 	        text-decoration: overline wavy pink;
 	text-decoration-thickness: 3px;
 }
+
+[dir="ltr"] .stage__container {
+	left: 1rem;
+	left: var(--size, 1rem);
+}
+
+[dir="rtl"] .stage__container {
+	right: 1rem;
+	right: var(--size, 1rem);
+}
+
+[dir="ltr"] .stage__container {
+	left: 1rem;
+}
+
+[dir="rtl"] .stage__container {
+	right: 1rem;
+}
diff --git a/plugin-packs/postcss-preset-env/test/basic.nesting.true.expect.css b/plugin-packs/postcss-preset-env/test/basic.nesting.true.expect.css
index 51505321b..9148b8bcf 100644
--- a/plugin-packs/postcss-preset-env/test/basic.nesting.true.expect.css
+++ b/plugin-packs/postcss-preset-env/test/basic.nesting.true.expect.css
@@ -420,3 +420,7 @@
 	-webkit-text-decoration: 3px wavy pink overline;
 	        text-decoration: 3px wavy pink overline;
 }
+
+.stage__container {
+	inset-inline-start: var(--size, 1rem);
+}
diff --git a/plugin-packs/postcss-preset-env/test/basic.op_mini.expect.css b/plugin-packs/postcss-preset-env/test/basic.op_mini.expect.css
index d91758c5c..b3e88b698 100644
--- a/plugin-packs/postcss-preset-env/test/basic.op_mini.expect.css
+++ b/plugin-packs/postcss-preset-env/test/basic.op_mini.expect.css
@@ -614,3 +614,21 @@ h1.test-custom-selectors,h2.test-custom-selectors,h3.test-custom-selectors,h4.te
 	text-decoration: overline wavy pink;
 	text-decoration-thickness: 3px;
 }
+
+[dir="ltr"] .stage__container {
+	left: 1rem;
+	left: var(--size, 1rem);
+}
+
+[dir="rtl"] .stage__container {
+	right: 1rem;
+	right: var(--size, 1rem);
+}
+
+[dir="ltr"] .stage__container {
+	left: 1rem;
+}
+
+[dir="rtl"] .stage__container {
+	right: 1rem;
+}
diff --git a/plugin-packs/postcss-preset-env/test/basic.preserve.true.expect.css b/plugin-packs/postcss-preset-env/test/basic.preserve.true.expect.css
index fb597973e..cde0faaee 100644
--- a/plugin-packs/postcss-preset-env/test/basic.preserve.true.expect.css
+++ b/plugin-packs/postcss-preset-env/test/basic.preserve.true.expect.css
@@ -1070,3 +1070,54 @@ h1.test-custom-selectors,h2.test-custom-selectors,h3.test-custom-selectors,h4.te
 	   -moz-text-decoration: 3px wavy pink overline;
 	        text-decoration: 3px wavy pink overline;
 }
+
+[dir="ltr"] .stage__container {
+	left: 1rem;
+	left: var(--size, 1rem);
+}
+
+[dir="ltr"] .stage__container {
+	left: 1rem;
+	left: var(--size, 1rem);
+}
+
+.stage__container:dir(ltr) {
+	left: 1rem;
+	left: var(--size, 1rem);
+}
+
+[dir="rtl"] .stage__container {
+	right: 1rem;
+	right: var(--size, 1rem);
+}
+
+[dir="rtl"] .stage__container {
+	right: 1rem;
+	right: var(--size, 1rem);
+}
+
+.stage__container:dir(rtl) {
+	right: 1rem;
+	right: var(--size, 1rem);
+}
+
+[dir="ltr"] .stage__container {
+	left: 1rem;
+}
+
+.stage__container:dir(ltr) {
+	left: 1rem;
+}
+
+[dir="rtl"] .stage__container {
+	right: 1rem;
+}
+
+.stage__container:dir(rtl) {
+	right: 1rem;
+}
+
+.stage__container {
+	inset-inline-start: 1rem;
+	inset-inline-start: var(--size, 1rem);
+}
diff --git a/plugin-packs/postcss-preset-env/test/basic.safari15.expect.css b/plugin-packs/postcss-preset-env/test/basic.safari15.expect.css
index 552f859d5..ec5ff10a5 100644
--- a/plugin-packs/postcss-preset-env/test/basic.safari15.expect.css
+++ b/plugin-packs/postcss-preset-env/test/basic.safari15.expect.css
@@ -452,3 +452,7 @@
 	text-decoration: overline wavy pink;
 	text-decoration-thickness: 3px;
 }
+
+.stage__container {
+	inset-inline-start: var(--size, 1rem);
+}
diff --git a/plugin-packs/postcss-preset-env/test/basic.stage0-ff49.expect.css b/plugin-packs/postcss-preset-env/test/basic.stage0-ff49.expect.css
index a9734c513..d1c2ac2f6 100644
--- a/plugin-packs/postcss-preset-env/test/basic.stage0-ff49.expect.css
+++ b/plugin-packs/postcss-preset-env/test/basic.stage0-ff49.expect.css
@@ -525,3 +525,11 @@ h1.test-custom-selectors,h2.test-custom-selectors,h3.test-custom-selectors,h4.te
 	text-decoration: overline wavy pink;
 	text-decoration-thickness: 3px;
 }
+
+.stage__container:dir(ltr) {
+	left: var(--size, 1rem);
+}
+
+.stage__container:dir(rtl) {
+	right: var(--size, 1rem);
+}
diff --git a/plugin-packs/postcss-preset-env/test/basic.stage0-ff66.expect.css b/plugin-packs/postcss-preset-env/test/basic.stage0-ff66.expect.css
index ce9d5f172..942a43c2e 100644
--- a/plugin-packs/postcss-preset-env/test/basic.stage0-ff66.expect.css
+++ b/plugin-packs/postcss-preset-env/test/basic.stage0-ff66.expect.css
@@ -506,3 +506,7 @@ h1.test-custom-selectors,h2.test-custom-selectors,h3.test-custom-selectors,h4.te
 	text-decoration: overline wavy pink;
 	text-decoration-thickness: 3px;
 }
+
+.stage__container {
+	inset-inline-start: var(--size, 1rem);
+}
diff --git a/plugin-packs/postcss-preset-env/test/basic.stage0.expect.css b/plugin-packs/postcss-preset-env/test/basic.stage0.expect.css
index 6479f5f6a..caadcfd77 100644
--- a/plugin-packs/postcss-preset-env/test/basic.stage0.expect.css
+++ b/plugin-packs/postcss-preset-env/test/basic.stage0.expect.css
@@ -636,3 +636,21 @@ h1.test-custom-selectors,h2.test-custom-selectors,h3.test-custom-selectors,h4.te
 	        text-decoration: overline wavy pink;
 	text-decoration-thickness: 3px;
 }
+
+[dir="ltr"] .stage__container {
+	left: 1rem;
+	left: var(--size, 1rem);
+}
+
+[dir="rtl"] .stage__container {
+	right: 1rem;
+	right: var(--size, 1rem);
+}
+
+[dir="ltr"] .stage__container {
+	left: 1rem;
+}
+
+[dir="rtl"] .stage__container {
+	right: 1rem;
+}
diff --git a/plugin-packs/postcss-preset-env/test/basic.vendors-1.expect.css b/plugin-packs/postcss-preset-env/test/basic.vendors-1.expect.css
index c154a8c66..621cfcb2d 100644
--- a/plugin-packs/postcss-preset-env/test/basic.vendors-1.expect.css
+++ b/plugin-packs/postcss-preset-env/test/basic.vendors-1.expect.css
@@ -613,3 +613,21 @@
 	        text-decoration: overline wavy pink;
 	text-decoration-thickness: 3px;
 }
+
+[dir="ltr"] .stage__container {
+	left: 1rem;
+	left: var(--size, 1rem);
+}
+
+[dir="rtl"] .stage__container {
+	right: 1rem;
+	right: var(--size, 1rem);
+}
+
+[dir="ltr"] .stage__container {
+	left: 1rem;
+}
+
+[dir="rtl"] .stage__container {
+	right: 1rem;
+}
diff --git a/plugin-packs/postcss-preset-env/test/basic.vendors-2.expect.css b/plugin-packs/postcss-preset-env/test/basic.vendors-2.expect.css
index 70bd47030..b81e2f17d 100644
--- a/plugin-packs/postcss-preset-env/test/basic.vendors-2.expect.css
+++ b/plugin-packs/postcss-preset-env/test/basic.vendors-2.expect.css
@@ -576,3 +576,21 @@
 	        text-decoration: overline wavy pink;
 	text-decoration-thickness: 3px;
 }
+
+.stage__container:dir(ltr) {
+	left: 1rem;
+	left: var(--size, 1rem);
+}
+
+.stage__container:dir(rtl) {
+	right: 1rem;
+	right: var(--size, 1rem);
+}
+
+.stage__container:dir(ltr) {
+	left: 1rem;
+}
+
+.stage__container:dir(rtl) {
+	right: 1rem;
+}
diff --git a/plugin-packs/postcss-preset-env/test/basic.vendors-3.expect.css b/plugin-packs/postcss-preset-env/test/basic.vendors-3.expect.css
index 223d5fead..e13550bf7 100644
--- a/plugin-packs/postcss-preset-env/test/basic.vendors-3.expect.css
+++ b/plugin-packs/postcss-preset-env/test/basic.vendors-3.expect.css
@@ -547,3 +547,21 @@
 	-webkit-text-decoration: 3px wavy pink overline;
 	        text-decoration: 3px wavy pink overline;
 }
+
+.stage__container:dir(ltr) {
+	left: 1rem;
+	left: var(--size, 1rem);
+}
+
+.stage__container:dir(rtl) {
+	right: 1rem;
+	right: var(--size, 1rem);
+}
+
+.stage__container:dir(ltr) {
+	left: 1rem;
+}
+
+.stage__container:dir(rtl) {
+	right: 1rem;
+}
diff --git a/plugins/postcss-custom-properties/CHANGELOG.md b/plugins/postcss-custom-properties/CHANGELOG.md
index ac8027742..80338ad50 100644
--- a/plugins/postcss-custom-properties/CHANGELOG.md
+++ b/plugins/postcss-custom-properties/CHANGELOG.md
@@ -1,5 +1,24 @@
 # Changes to PostCSS Custom Properties
 
+### Unreleased
+
+- Prevent duplicate code generation.
+
+```diff
+.foo {
+	order: 1;
+	order: var(--my-order, 1);
+}
+
+/* becomes */
+
+.foo {
+	order: 1;
+- 	order: 1;
+	order: var(--my-order, 1);
+}
+```
+
 ### 12.1.8 (June 10, 2022)
 
 - Remove some unneeded regular expressions.
diff --git a/plugins/postcss-custom-properties/src/lib/transform-properties.ts b/plugins/postcss-custom-properties/src/lib/transform-properties.ts
index fe09c4e36..e78296b04 100644
--- a/plugins/postcss-custom-properties/src/lib/transform-properties.ts
+++ b/plugins/postcss-custom-properties/src/lib/transform-properties.ts
@@ -1,6 +1,7 @@
 import valuesParser from 'postcss-value-parser';
 import transformValueAST from './transform-value-ast';
 import { isRuleIgnored } from './is-ignored';
+import { Declaration } from 'postcss';
 
 // transform custom pseudo selectors with custom selectors
 export default (decl, customProperties, opts) => {
@@ -20,6 +21,10 @@ export default (decl, customProperties, opts) => {
 
 		// conditionally transform values that have changed
 		if (value !== originalValue) {
+			if (parentHasExactFallback(decl, value)) {
+				return;
+			}
+
 			if (opts.preserve) {
 				const beforeDecl = decl.cloneBefore({ value });
 
@@ -47,3 +52,31 @@ const isTransformableDecl = decl => !decl.variable && decl.value.includes('--')
 // whether the declaration has a trailing comment
 const hasTrailingComment = decl => 'value' in Object(Object(decl.raws).value) && 'raw' in decl.raws.value && trailingCommentRegExp.test(decl.raws.value.raw);
 const trailingCommentRegExp = /^([\W\w]+)(\s*\/\*[\W\w]+?\*\/)$/;
+
+function parentHasExactFallback(decl: Declaration, value: string): boolean {
+	if (!decl || !decl.parent) {
+		return false;
+	}
+
+	let hasFallback = false;
+	const declIndex = decl.parent.index(decl);
+	decl.parent.each((sibling, index) => {
+		if (sibling === decl) {
+			return false;
+		}
+
+		if (index >= declIndex) {
+			return false;
+		}
+
+		if (sibling.type !== 'decl') {
+			return;
+		}
+
+		if (sibling.prop.toLowerCase() === decl.prop.toLowerCase() && sibling.value === value) {
+			hasFallback = true;
+		}
+	});
+
+	return hasFallback;
+}
diff --git a/plugins/postcss-custom-properties/test/basic.css b/plugins/postcss-custom-properties/test/basic.css
index 92d7a27be..99f3ec38c 100644
--- a/plugins/postcss-custom-properties/test/basic.css
+++ b/plugins/postcss-custom-properties/test/basic.css
@@ -138,3 +138,13 @@ html {
 .test {
 	font-family: var(--font, "Helvetica Neue", Arial, sans-serif);
 }
+
+.ignores-declarations-that-have-an-exact-fallback {
+	left: 1rem;
+	left: var(--size, 1rem);
+}
+
+.does-not-ignore-declarations-that-have-an-exact-override {
+	left: var(--size, 1rem);
+	left: 1rem;
+}
diff --git a/plugins/postcss-custom-properties/test/basic.expect.css b/plugins/postcss-custom-properties/test/basic.expect.css
index adbdb21f5..169d4d2a9 100644
--- a/plugins/postcss-custom-properties/test/basic.expect.css
+++ b/plugins/postcss-custom-properties/test/basic.expect.css
@@ -159,3 +159,14 @@ html {
 	font-family: "Helvetica Neue", Arial, sans-serif;
 	font-family: var(--font, "Helvetica Neue", Arial, sans-serif);
 }
+
+.ignores-declarations-that-have-an-exact-fallback {
+	left: 1rem;
+	left: var(--size, 1rem);
+}
+
+.does-not-ignore-declarations-that-have-an-exact-override {
+	left: 1rem;
+	left: var(--size, 1rem);
+	left: 1rem;
+}
diff --git a/plugins/postcss-custom-properties/test/basic.import-is-empty.expect.css b/plugins/postcss-custom-properties/test/basic.import-is-empty.expect.css
index adbdb21f5..169d4d2a9 100644
--- a/plugins/postcss-custom-properties/test/basic.import-is-empty.expect.css
+++ b/plugins/postcss-custom-properties/test/basic.import-is-empty.expect.css
@@ -159,3 +159,14 @@ html {
 	font-family: "Helvetica Neue", Arial, sans-serif;
 	font-family: var(--font, "Helvetica Neue", Arial, sans-serif);
 }
+
+.ignores-declarations-that-have-an-exact-fallback {
+	left: 1rem;
+	left: var(--size, 1rem);
+}
+
+.does-not-ignore-declarations-that-have-an-exact-override {
+	left: 1rem;
+	left: var(--size, 1rem);
+	left: 1rem;
+}
diff --git a/plugins/postcss-custom-properties/test/basic.import-override.expect.css b/plugins/postcss-custom-properties/test/basic.import-override.expect.css
index cd0423d57..3cbb7fd22 100644
--- a/plugins/postcss-custom-properties/test/basic.import-override.expect.css
+++ b/plugins/postcss-custom-properties/test/basic.import-override.expect.css
@@ -109,3 +109,13 @@
 .test {
 	font-family: "Helvetica Neue", Arial, sans-serif;
 }
+
+.ignores-declarations-that-have-an-exact-fallback {
+	left: 1rem;
+	left: var(--size, 1rem);
+}
+
+.does-not-ignore-declarations-that-have-an-exact-override {
+	left: 1rem;
+	left: 1rem;
+}
diff --git a/plugins/postcss-custom-properties/test/basic.import-override.inverse.expect.css b/plugins/postcss-custom-properties/test/basic.import-override.inverse.expect.css
index 8f9292457..fc55c93ac 100644
--- a/plugins/postcss-custom-properties/test/basic.import-override.inverse.expect.css
+++ b/plugins/postcss-custom-properties/test/basic.import-override.inverse.expect.css
@@ -109,3 +109,13 @@
 .test {
 	font-family: "Helvetica Neue", Arial, sans-serif;
 }
+
+.ignores-declarations-that-have-an-exact-fallback {
+	left: 1rem;
+	left: var(--size, 1rem);
+}
+
+.does-not-ignore-declarations-that-have-an-exact-override {
+	left: 1rem;
+	left: 1rem;
+}
diff --git a/plugins/postcss-custom-properties/test/basic.import.expect.css b/plugins/postcss-custom-properties/test/basic.import.expect.css
index cbb490f97..b003abd32 100644
--- a/plugins/postcss-custom-properties/test/basic.import.expect.css
+++ b/plugins/postcss-custom-properties/test/basic.import.expect.css
@@ -160,3 +160,14 @@ html {
 	font-family: "Helvetica Neue", Arial, sans-serif;
 	font-family: var(--font, "Helvetica Neue", Arial, sans-serif);
 }
+
+.ignores-declarations-that-have-an-exact-fallback {
+	left: 1rem;
+	left: var(--size, 1rem);
+}
+
+.does-not-ignore-declarations-that-have-an-exact-override {
+	left: 1rem;
+	left: var(--size, 1rem);
+	left: 1rem;
+}
diff --git a/plugins/postcss-custom-properties/test/basic.preserve.expect.css b/plugins/postcss-custom-properties/test/basic.preserve.expect.css
index 01b766559..b8bfc6a85 100644
--- a/plugins/postcss-custom-properties/test/basic.preserve.expect.css
+++ b/plugins/postcss-custom-properties/test/basic.preserve.expect.css
@@ -109,3 +109,13 @@
 .test {
 	font-family: "Helvetica Neue", Arial, sans-serif;
 }
+
+.ignores-declarations-that-have-an-exact-fallback {
+	left: 1rem;
+	left: var(--size, 1rem);
+}
+
+.does-not-ignore-declarations-that-have-an-exact-override {
+	left: 1rem;
+	left: 1rem;
+}