diff --git a/src/main/kotlin/org/koitharu/kotatsu/parsers/model/Constants.kt b/src/main/kotlin/org/koitharu/kotatsu/parsers/model/Constants.kt
index b98ce963..a1ed22c8 100644
--- a/src/main/kotlin/org/koitharu/kotatsu/parsers/model/Constants.kt
+++ b/src/main/kotlin/org/koitharu/kotatsu/parsers/model/Constants.kt
@@ -2,4 +2,10 @@
 
 package org.koitharu.kotatsu.parsers.model
 
-const val RATING_UNKNOWN = -1f
\ No newline at end of file
+public const val RATING_UNKNOWN: Float = -1f
+
+public const val YEAR_UNKNOWN: Int = 0
+
+public const val YEAR_MIN: Int = 1900
+
+public const val YEAR_MAX: Int = 2099
diff --git a/src/main/kotlin/org/koitharu/kotatsu/parsers/model/MangaListFilter.kt b/src/main/kotlin/org/koitharu/kotatsu/parsers/model/MangaListFilter.kt
index a90a9169..c6c7d2d1 100644
--- a/src/main/kotlin/org/koitharu/kotatsu/parsers/model/MangaListFilter.kt
+++ b/src/main/kotlin/org/koitharu/kotatsu/parsers/model/MangaListFilter.kt
@@ -12,9 +12,9 @@ public data class MangaListFilter(
 	@JvmField val contentRating: Set<ContentRating> = emptySet(),
 	@JvmField val types: Set<ContentType> = emptySet(),
 	@JvmField val demographics: Set<Demographic> = emptySet(),
-	@JvmField val year: Int = 0,
-	@JvmField val yearFrom: Int = 0,
-	@JvmField val yearTo: Int = 0,
+	@JvmField val year: Int = YEAR_UNKNOWN,
+	@JvmField val yearFrom: Int = YEAR_UNKNOWN,
+	@JvmField val yearTo: Int = YEAR_UNKNOWN,
 ) {
 
 	public fun isEmpty(): Boolean = tags.isEmpty() &&
@@ -24,9 +24,9 @@ public data class MangaListFilter(
 		states.isEmpty() &&
 		contentRating.isEmpty() &&
 		query == null &&
-		year == 0 &&
-		yearFrom == 0 &&
-		yearTo == 0 &&
+		year == YEAR_UNKNOWN &&
+		yearFrom == YEAR_UNKNOWN &&
+		yearTo == YEAR_UNKNOWN &&
 		types.isEmpty() &&
 		demographics.isEmpty()
 
diff --git a/src/main/kotlin/org/koitharu/kotatsu/parsers/site/all/ComickFunParser.kt b/src/main/kotlin/org/koitharu/kotatsu/parsers/site/all/ComickFunParser.kt
index c514ea49..890c2d1e 100644
--- a/src/main/kotlin/org/koitharu/kotatsu/parsers/site/all/ComickFunParser.kt
+++ b/src/main/kotlin/org/koitharu/kotatsu/parsers/site/all/ComickFunParser.kt
@@ -107,11 +107,11 @@ internal class ComickFunParser(context: MangaLoaderContext) :
 					)
 				}
 
-				if (filter.yearFrom != 0) {
+				if (filter.yearFrom != YEAR_UNKNOWN) {
 					url.addQueryParameter("from", filter.yearFrom.toString())
 				}
 
-				if (filter.yearTo != 0) {
+				if (filter.yearTo != YEAR_UNKNOWN) {
 					url.addQueryParameter("to", filter.yearTo.toString())
 				}
 
diff --git a/src/main/kotlin/org/koitharu/kotatsu/parsers/site/ru/grouple/GroupleParser.kt b/src/main/kotlin/org/koitharu/kotatsu/parsers/site/ru/grouple/GroupleParser.kt
index cdb6a14e..6b59fd1b 100644
--- a/src/main/kotlin/org/koitharu/kotatsu/parsers/site/ru/grouple/GroupleParser.kt
+++ b/src/main/kotlin/org/koitharu/kotatsu/parsers/site/ru/grouple/GroupleParser.kt
@@ -361,9 +361,9 @@ internal abstract class GroupleParser(
 		payload["s_wait_upload"] = ""
 		payload["s_sale"] = ""
 		payload["years"] = buildString {
-			append(filter.yearFrom.ifZero { 1900 })
+			append(filter.yearFrom.ifZero { YEAR_MIN })
 			append(',')
-			append(filter.yearTo.ifZero { 2099 })
+			append(filter.yearTo.ifZero { YEAR_MAX })
 		}
 		payload["+"] = "Искать".urlEncoded()
 		return webClient.httpPost(url, payload)