diff --git a/packages/core/src/vivliostyle/css-cascade.ts b/packages/core/src/vivliostyle/css-cascade.ts
index 1c229db22..8ffa8fb07 100644
--- a/packages/core/src/vivliostyle/css-cascade.ts
+++ b/packages/core/src/vivliostyle/css-cascade.ts
@@ -383,11 +383,11 @@ export function isSpecialName(name: string): boolean {
 }
 
 export function isMapName(name: string): boolean {
-  return name.charAt(0) == "_";
+  return name.charAt(0) === "_" && name !== "_viewConditionalStyles";
 }
 
 export function isPropName(name: string): boolean {
-  return name.charAt(0) != "_" && !SPECIALS[name];
+  return name.charAt(0) !== "_" && !SPECIALS[name];
 }
 
 export function isInherited(name: string): boolean {