diff --git a/src/main/java/com/commafeed/backend/feed/EstimateDirection.java b/src/main/java/com/commafeed/backend/feed/EstimateDirection.java
index f2ca42f3..8fdcf662 100644
--- a/src/main/java/com/commafeed/backend/feed/EstimateDirection.java
+++ b/src/main/java/com/commafeed/backend/feed/EstimateDirection.java
@@ -10,9 +10,9 @@ import java.util.regex.Pattern;
 class EstimateDirection {
 	private static final float RTL_DETECTION_THRESHOLD = 0.40f;
 
-	private static volatile String LTR_CHARS = "A-Za-z\u00C0-\u00D6\u00D8-\u00F6\u00F8-\u02B8\u0300-\u0590\u0800-\u1FFF"
+	private static final String LTR_CHARS = "A-Za-z\u00C0-\u00D6\u00D8-\u00F6\u00F8-\u02B8\u0300-\u0590\u0800-\u1FFF"
 			+ "\u2C00-\uFB1C\uFDFE-\uFE6F\uFEFD-\uFFFF";
-	private static volatile String RTL_CHARS = "\u0591-\u07FF\uFB1D-\uFDFD\uFE70-\uFEFC";
+	private static final String RTL_CHARS = "\u0591-\u07FF\uFB1D-\uFDFD\uFE70-\uFEFC";
 
 	private static final Pattern WORD_SEPARATOR_RE = Pattern.compile("\\s+");
 	private static final Pattern FIRST_STRONG_IS_RTL_RE = Pattern.compile("^[^" + LTR_CHARS + "]*[" + RTL_CHARS + ']');