diff --git a/internal/css_parser/css_decls.go b/internal/css_parser/css_decls.go
index ed17137780c..b3de8924241 100644
--- a/internal/css_parser/css_decls.go
+++ b/internal/css_parser/css_decls.go
@@ -77,13 +77,15 @@ func compactTokenQuad(a css_ast.Token, b css_ast.Token, c css_ast.Token, d css_a
 	return tokens
 }
 
-func (p *parser) processDeclarations(rules []css_ast.Rule) []css_ast.Rule {
+func (p *parser) processDeclarations(rules []css_ast.Rule) (rewrittenRules []css_ast.Rule) {
 	margin := boxTracker{key: css_ast.DMargin, keyText: "margin", allowAuto: true}
 	padding := boxTracker{key: css_ast.DPadding, keyText: "padding", allowAuto: false}
 	inset := boxTracker{key: css_ast.DInset, keyText: "inset", allowAuto: true}
 	borderRadius := borderRadiusTracker{}
+	rewrittenRules = make([]css_ast.Rule, 0, len(rules))
 
-	for i, rule := range rules {
+	for _, rule := range rules {
+		rewrittenRules = append(rewrittenRules, rule)
 		decl, ok := rule.Data.(*css_ast.RDeclaration)
 		if !ok {
 			continue
@@ -153,89 +155,89 @@ func (p *parser) processDeclarations(rules []css_ast.Rule) []css_ast.Rule {
 		// Margin
 		case css_ast.DMargin:
 			if p.options.MinifySyntax {
-				margin.mangleSides(rules, decl, i, p.options.MinifyWhitespace)
+				margin.mangleSides(rewrittenRules, decl, p.options.MinifyWhitespace)
 			}
 		case css_ast.DMarginTop:
 			if p.options.MinifySyntax {
-				margin.mangleSide(rules, decl, i, p.options.MinifyWhitespace, boxTop)
+				margin.mangleSide(rewrittenRules, decl, p.options.MinifyWhitespace, boxTop)
 			}
 		case css_ast.DMarginRight:
 			if p.options.MinifySyntax {
-				margin.mangleSide(rules, decl, i, p.options.MinifyWhitespace, boxRight)
+				margin.mangleSide(rewrittenRules, decl, p.options.MinifyWhitespace, boxRight)
 			}
 		case css_ast.DMarginBottom:
 			if p.options.MinifySyntax {
-				margin.mangleSide(rules, decl, i, p.options.MinifyWhitespace, boxBottom)
+				margin.mangleSide(rewrittenRules, decl, p.options.MinifyWhitespace, boxBottom)
 			}
 		case css_ast.DMarginLeft:
 			if p.options.MinifySyntax {
-				margin.mangleSide(rules, decl, i, p.options.MinifyWhitespace, boxLeft)
+				margin.mangleSide(rewrittenRules, decl, p.options.MinifyWhitespace, boxLeft)
 			}
 
 		// Padding
 		case css_ast.DPadding:
 			if p.options.MinifySyntax {
-				padding.mangleSides(rules, decl, i, p.options.MinifyWhitespace)
+				padding.mangleSides(rewrittenRules, decl, p.options.MinifyWhitespace)
 			}
 		case css_ast.DPaddingTop:
 			if p.options.MinifySyntax {
-				padding.mangleSide(rules, decl, i, p.options.MinifyWhitespace, boxTop)
+				padding.mangleSide(rewrittenRules, decl, p.options.MinifyWhitespace, boxTop)
 			}
 		case css_ast.DPaddingRight:
 			if p.options.MinifySyntax {
-				padding.mangleSide(rules, decl, i, p.options.MinifyWhitespace, boxRight)
+				padding.mangleSide(rewrittenRules, decl, p.options.MinifyWhitespace, boxRight)
 			}
 		case css_ast.DPaddingBottom:
 			if p.options.MinifySyntax {
-				padding.mangleSide(rules, decl, i, p.options.MinifyWhitespace, boxBottom)
+				padding.mangleSide(rewrittenRules, decl, p.options.MinifyWhitespace, boxBottom)
 			}
 		case css_ast.DPaddingLeft:
 			if p.options.MinifySyntax {
-				padding.mangleSide(rules, decl, i, p.options.MinifyWhitespace, boxLeft)
+				padding.mangleSide(rewrittenRules, decl, p.options.MinifyWhitespace, boxLeft)
 			}
 
 		// Inset
 		case css_ast.DInset:
 			if !p.options.UnsupportedCSSFeatures.Has(compat.InsetProperty) && p.options.MinifySyntax {
-				inset.mangleSides(rules, decl, i, p.options.MinifyWhitespace)
+				inset.mangleSides(rewrittenRules, decl, p.options.MinifyWhitespace)
 			}
 		case css_ast.DTop:
 			if !p.options.UnsupportedCSSFeatures.Has(compat.InsetProperty) && p.options.MinifySyntax {
-				inset.mangleSide(rules, decl, i, p.options.MinifyWhitespace, boxTop)
+				inset.mangleSide(rewrittenRules, decl, p.options.MinifyWhitespace, boxTop)
 			}
 		case css_ast.DRight:
 			if !p.options.UnsupportedCSSFeatures.Has(compat.InsetProperty) && p.options.MinifySyntax {
-				inset.mangleSide(rules, decl, i, p.options.MinifyWhitespace, boxRight)
+				inset.mangleSide(rewrittenRules, decl, p.options.MinifyWhitespace, boxRight)
 			}
 		case css_ast.DBottom:
 			if !p.options.UnsupportedCSSFeatures.Has(compat.InsetProperty) && p.options.MinifySyntax {
-				inset.mangleSide(rules, decl, i, p.options.MinifyWhitespace, boxBottom)
+				inset.mangleSide(rewrittenRules, decl, p.options.MinifyWhitespace, boxBottom)
 			}
 		case css_ast.DLeft:
 			if !p.options.UnsupportedCSSFeatures.Has(compat.InsetProperty) && p.options.MinifySyntax {
-				inset.mangleSide(rules, decl, i, p.options.MinifyWhitespace, boxLeft)
+				inset.mangleSide(rewrittenRules, decl, p.options.MinifyWhitespace, boxLeft)
 			}
 
 		// Border radius
 		case css_ast.DBorderRadius:
 			if p.options.MinifySyntax {
-				borderRadius.mangleCorners(rules, decl, i, p.options.MinifyWhitespace)
+				borderRadius.mangleCorners(rewrittenRules, decl, p.options.MinifyWhitespace)
 			}
 		case css_ast.DBorderTopLeftRadius:
 			if p.options.MinifySyntax {
-				borderRadius.mangleCorner(rules, decl, i, p.options.MinifyWhitespace, borderRadiusTopLeft)
+				borderRadius.mangleCorner(rewrittenRules, decl, p.options.MinifyWhitespace, borderRadiusTopLeft)
 			}
 		case css_ast.DBorderTopRightRadius:
 			if p.options.MinifySyntax {
-				borderRadius.mangleCorner(rules, decl, i, p.options.MinifyWhitespace, borderRadiusTopRight)
+				borderRadius.mangleCorner(rewrittenRules, decl, p.options.MinifyWhitespace, borderRadiusTopRight)
 			}
 		case css_ast.DBorderBottomRightRadius:
 			if p.options.MinifySyntax {
-				borderRadius.mangleCorner(rules, decl, i, p.options.MinifyWhitespace, borderRadiusBottomRight)
+				borderRadius.mangleCorner(rewrittenRules, decl, p.options.MinifyWhitespace, borderRadiusBottomRight)
 			}
 		case css_ast.DBorderBottomLeftRadius:
 			if p.options.MinifySyntax {
-				borderRadius.mangleCorner(rules, decl, i, p.options.MinifyWhitespace, borderRadiusBottomLeft)
+				borderRadius.mangleCorner(rewrittenRules, decl, p.options.MinifyWhitespace, borderRadiusBottomLeft)
 			}
 		}
 	}
@@ -243,14 +245,14 @@ func (p *parser) processDeclarations(rules []css_ast.Rule) []css_ast.Rule {
 	// Compact removed rules
 	if p.options.MinifySyntax {
 		end := 0
-		for _, rule := range rules {
+		for _, rule := range rewrittenRules {
 			if rule.Data != nil {
-				rules[end] = rule
+				rewrittenRules[end] = rule
 				end++
 			}
 		}
-		rules = rules[:end]
+		rewrittenRules = rewrittenRules[:end]
 	}
 
-	return rules
+	return
 }
diff --git a/internal/css_parser/css_decls_border_radius.go b/internal/css_parser/css_decls_border_radius.go
index bba664a62d9..9b40dbfdb01 100644
--- a/internal/css_parser/css_decls_border_radius.go
+++ b/internal/css_parser/css_decls_border_radius.go
@@ -35,7 +35,7 @@ func (borderRadius *borderRadiusTracker) updateCorner(rules []css_ast.Rule, corn
 	borderRadius.corners[corner] = new
 }
 
-func (borderRadius *borderRadiusTracker) mangleCorners(rules []css_ast.Rule, decl *css_ast.RDeclaration, index int, minifyWhitespace bool) {
+func (borderRadius *borderRadiusTracker) mangleCorners(rules []css_ast.Rule, decl *css_ast.RDeclaration, minifyWhitespace bool) {
 	// Reset if we see a change in the "!important" flag
 	if borderRadius.important != decl.Important {
 		borderRadius.corners = [4]borderRadiusCorner{}
@@ -87,7 +87,7 @@ func (borderRadius *borderRadiusTracker) mangleCorners(rules []css_ast.Rule, dec
 			firstToken:  t,
 			secondToken: t,
 			unitSafety:  unitSafety,
-			ruleIndex:   uint32(index),
+			ruleIndex:   uint32(len(rules) - 1),
 		})
 	}
 
@@ -105,7 +105,7 @@ func (borderRadius *borderRadiusTracker) mangleCorners(rules []css_ast.Rule, dec
 	borderRadius.compactRules(rules, decl.KeyRange, minifyWhitespace)
 }
 
-func (borderRadius *borderRadiusTracker) mangleCorner(rules []css_ast.Rule, decl *css_ast.RDeclaration, index int, minifyWhitespace bool, corner int) {
+func (borderRadius *borderRadiusTracker) mangleCorner(rules []css_ast.Rule, decl *css_ast.RDeclaration, minifyWhitespace bool, corner int) {
 	// Reset if we see a change in the "!important" flag
 	if borderRadius.important != decl.Important {
 		borderRadius.corners = [4]borderRadiusCorner{}
@@ -145,7 +145,7 @@ func (borderRadius *borderRadiusTracker) mangleCorner(rules []css_ast.Rule, decl
 			firstToken:    firstToken,
 			secondToken:   secondToken,
 			unitSafety:    unitSafety,
-			ruleIndex:     uint32(index),
+			ruleIndex:     uint32(len(rules) - 1),
 			wasSingleRule: true,
 		})
 		borderRadius.compactRules(rules, decl.KeyRange, minifyWhitespace)
diff --git a/internal/css_parser/css_decls_box.go b/internal/css_parser/css_decls_box.go
index 75f7afa7436..ba60672f088 100644
--- a/internal/css_parser/css_decls_box.go
+++ b/internal/css_parser/css_decls_box.go
@@ -91,7 +91,7 @@ func (box *boxTracker) updateSide(rules []css_ast.Rule, side int, new boxSide) {
 	box.sides[side] = new
 }
 
-func (box *boxTracker) mangleSides(rules []css_ast.Rule, decl *css_ast.RDeclaration, index int, minifyWhitespace bool) {
+func (box *boxTracker) mangleSides(rules []css_ast.Rule, decl *css_ast.RDeclaration, minifyWhitespace bool) {
 	// Reset if we see a change in the "!important" flag
 	if box.important != decl.Important {
 		box.sides = [4]boxSide{}
@@ -116,7 +116,7 @@ func (box *boxTracker) mangleSides(rules []css_ast.Rule, decl *css_ast.RDeclarat
 			}
 			box.updateSide(rules, side, boxSide{
 				token:      t,
-				ruleIndex:  uint32(index),
+				ruleIndex:  uint32(len(rules) - 1),
 				unitSafety: unitSafety,
 			})
 		}
@@ -126,7 +126,7 @@ func (box *boxTracker) mangleSides(rules []css_ast.Rule, decl *css_ast.RDeclarat
 	}
 }
 
-func (box *boxTracker) mangleSide(rules []css_ast.Rule, decl *css_ast.RDeclaration, index int, minifyWhitespace bool, side int) {
+func (box *boxTracker) mangleSide(rules []css_ast.Rule, decl *css_ast.RDeclaration, minifyWhitespace bool, side int) {
 	// Reset if we see a change in the "!important" flag
 	if box.important != decl.Important {
 		box.sides = [4]boxSide{}
@@ -144,7 +144,7 @@ func (box *boxTracker) mangleSide(rules []css_ast.Rule, decl *css_ast.RDeclarati
 			}
 			box.updateSide(rules, side, boxSide{
 				token:         t,
-				ruleIndex:     uint32(index),
+				ruleIndex:     uint32(len(rules) - 1),
 				wasSingleRule: true,
 				unitSafety:    unitSafety,
 			})