diff --git a/app/build.gradle b/app/build.gradle
index d81bce6d9..64aab0ef4 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -15,8 +15,8 @@ android {
 		applicationId 'org.koitharu.kotatsu'
 		minSdkVersion 21
 		targetSdkVersion 33
-		versionCode 545
-		versionName '5.1.1'
+		versionCode 546
+		versionName '5.1.2'
 		generatedDensities = []
 		testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
 
@@ -79,7 +79,7 @@ afterEvaluate {
 }
 dependencies {
 	//noinspection GradleDependency
-	implementation('com.github.KotatsuApp:kotatsu-parsers:cae7073f87') {
+	implementation('com.github.KotatsuApp:kotatsu-parsers:ebcc6391d6') {
 		exclude group: 'org.json', module: 'json'
 	}
 
diff --git a/app/src/main/kotlin/org/koitharu/kotatsu/settings/HeaderValidator.kt b/app/src/main/kotlin/org/koitharu/kotatsu/settings/HeaderValidator.kt
new file mode 100644
index 000000000..b25be70d6
--- /dev/null
+++ b/app/src/main/kotlin/org/koitharu/kotatsu/settings/HeaderValidator.kt
@@ -0,0 +1,27 @@
+package org.koitharu.kotatsu.settings
+
+import okhttp3.Headers
+import org.koitharu.kotatsu.R
+import org.koitharu.kotatsu.core.network.CommonHeaders
+import org.koitharu.kotatsu.core.util.EditTextValidator
+
+class HeaderValidator : EditTextValidator() {
+
+	private val headers = Headers.Builder()
+
+	override fun validate(text: String): ValidationResult {
+		val trimmed = text.trim()
+		if (trimmed.isEmpty()) {
+			return ValidationResult.Success
+		}
+		return if (!validateImpl(trimmed)) {
+			ValidationResult.Failed(context.getString(R.string.invalid_value_message))
+		} else {
+			ValidationResult.Success
+		}
+	}
+
+	private fun validateImpl(value: String): Boolean = runCatching {
+		headers[CommonHeaders.USER_AGENT] = value
+	}.isSuccess
+}
diff --git a/app/src/main/kotlin/org/koitharu/kotatsu/settings/SourceSettingsExt.kt b/app/src/main/kotlin/org/koitharu/kotatsu/settings/SourceSettingsExt.kt
index 5137fe95e..293f4847d 100644
--- a/app/src/main/kotlin/org/koitharu/kotatsu/settings/SourceSettingsExt.kt
+++ b/app/src/main/kotlin/org/koitharu/kotatsu/settings/SourceSettingsExt.kt
@@ -44,7 +44,7 @@ fun PreferenceFragmentCompat.addPreferencesFromRepository(repository: RemoteMang
 						EditTextBindListener(
 							inputType = EditorInfo.TYPE_CLASS_TEXT,
 							hint = key.defaultValue,
-							validator = null,
+							validator = HeaderValidator(),
 						),
 					)
 					setTitle(R.string.user_agent)
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index 2a5de47a9..aee909a83 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -423,4 +423,5 @@
 	<string name="address">Address</string>
 	<string name="port">Port</string>
 	<string name="proxy">Proxy</string>
+	<string name="invalid_value_message">Invalid value</string>
 </resources>