diff --git a/logstash-core/src/main/java/org/logstash/ConvertedMap.java b/logstash-core/src/main/java/org/logstash/ConvertedMap.java
index 2cf235889..99d33a926 100644
--- a/logstash-core/src/main/java/org/logstash/ConvertedMap.java
+++ b/logstash-core/src/main/java/org/logstash/ConvertedMap.java
@@ -99,6 +99,6 @@ public final class ConvertedMap extends IdentityHashMap<String, Object> {
      * @return Interned String
      */
     private static String convertKey(final RubyString key) {
-        return FieldReference.from(key.getByteList()).getKey();
+        return FieldReference.from(key).getKey();
     }
 }
diff --git a/logstash-core/src/main/java/org/logstash/FieldReference.java b/logstash-core/src/main/java/org/logstash/FieldReference.java
index ade18c419..041500a64 100644
--- a/logstash-core/src/main/java/org/logstash/FieldReference.java
+++ b/logstash-core/src/main/java/org/logstash/FieldReference.java
@@ -5,6 +5,7 @@ import java.util.Arrays;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
+import org.jruby.RubyString;
 
 public final class FieldReference {
 
@@ -41,9 +42,15 @@ public final class FieldReference {
         new FieldReference(EMPTY_STRING_ARRAY, Event.METADATA, META_PARENT);
 
     /**
-     * Cache of all existing {@link FieldReference}.
+     * Cache of all existing {@link FieldReference} by their {@link RubyString} source.
      */
-    private static final Map<CharSequence, FieldReference> CACHE =
+    private static final Map<RubyString, FieldReference> RUBY_CACHE =
+        new ConcurrentHashMap<>(64, 0.2F, 1);
+
+    /**
+     * Cache of all existing {@link FieldReference} by their {@link String} source.
+     */
+    private static final Map<String, FieldReference> CACHE =
         new ConcurrentHashMap<>(64, 0.2F, 1);
 
     private final String[] path;
@@ -65,7 +72,16 @@ public final class FieldReference {
         hash = calculateHash(this.key, this.path, this.type);
     }
 
-    public static FieldReference from(final CharSequence reference) {
+    public static FieldReference from(final RubyString reference) {
+        // atomicity between the get and put is not important
+        final FieldReference result = RUBY_CACHE.get(reference);
+        if (result != null) {
+            return result;
+        }
+        return RUBY_CACHE.computeIfAbsent(reference.newFrozen(), ref -> from(ref.asJavaString()));
+    }
+
+    public static FieldReference from(final String reference) {
         // atomicity between the get and put is not important
         final FieldReference result = CACHE.get(reference);
         if (result != null) {
@@ -138,7 +154,7 @@ public final class FieldReference {
         return prime * hash + type;
     }
 
-    private static FieldReference parseToCache(final CharSequence reference) {
+    private static FieldReference parseToCache(final String reference) {
         FieldReference result = parse(reference);
         if (CACHE.size() < 10_000) {
             result = deduplicate(result);
diff --git a/logstash-core/src/main/java/org/logstash/ext/JrubyEventExtLibrary.java b/logstash-core/src/main/java/org/logstash/ext/JrubyEventExtLibrary.java
index 6e2ec8548..debb83037 100644
--- a/logstash-core/src/main/java/org/logstash/ext/JrubyEventExtLibrary.java
+++ b/logstash-core/src/main/java/org/logstash/ext/JrubyEventExtLibrary.java
@@ -82,14 +82,14 @@ public final class JrubyEventExtLibrary {
         {
             return Rubyfier.deep(
                 context.runtime,
-                this.event.getUnconvertedField(FieldReference.from(reference.getByteList()))
+                this.event.getUnconvertedField(FieldReference.from(reference))
             );
         }
 
         @JRubyMethod(name = "set", required = 2)
         public IRubyObject ruby_set_field(ThreadContext context, RubyString reference, IRubyObject value)
         {
-            final FieldReference r = FieldReference.from(reference.getByteList());
+            final FieldReference r = FieldReference.from(reference);
             if (r.equals(FieldReference.TIMESTAMP_REFERENCE)) {
                 if (!(value instanceof JrubyTimestampExtLibrary.RubyTimestamp)) {
                     throw context.runtime.newTypeError("wrong argument type " + value.getMetaClass() + " (expected LogStash::Timestamp)");
@@ -124,7 +124,7 @@ public final class JrubyEventExtLibrary {
         @JRubyMethod(name = "include?", required = 1)
         public IRubyObject ruby_includes(ThreadContext context, RubyString reference) {
             return RubyBoolean.newBoolean(
-                context.runtime, this.event.includes(FieldReference.from(reference.getByteList()))
+                context.runtime, this.event.includes(FieldReference.from(reference))
             );
         }
 
@@ -132,7 +132,7 @@ public final class JrubyEventExtLibrary {
         public IRubyObject ruby_remove(ThreadContext context, RubyString reference) {
             return Rubyfier.deep(
                 context.runtime,
-                this.event.remove(FieldReference.from(reference.getByteList()))
+                this.event.remove(FieldReference.from(reference))
             );
         }
 
diff --git a/logstash-core/src/test/java/org/logstash/AccessorsTest.java b/logstash-core/src/test/java/org/logstash/AccessorsTest.java
index 51415979f..34751a0b8 100644
--- a/logstash-core/src/test/java/org/logstash/AccessorsTest.java
+++ b/logstash-core/src/test/java/org/logstash/AccessorsTest.java
@@ -194,20 +194,20 @@ public class AccessorsTest {
         set(data, "[foo][bar]", "Another String");
     }
 
-    private static Object get(final ConvertedMap data, final CharSequence reference) {
+    private static Object get(final ConvertedMap data, final String reference) {
         return Accessors.get(data, FieldReference.from(reference));
     }
 
-    private static Object set(final ConvertedMap data, final CharSequence reference,
+    private static Object set(final ConvertedMap data, final String reference,
         final Object value) {
         return Accessors.set(data, FieldReference.from(reference), value);
     }
 
-    private static Object del(final ConvertedMap data, final CharSequence reference) {
+    private static Object del(final ConvertedMap data, final String reference) {
         return Accessors.del(data, FieldReference.from(reference));
     }
 
-    private static boolean includes(final ConvertedMap data, final CharSequence reference) {
+    private static boolean includes(final ConvertedMap data, final String reference) {
         return Accessors.includes(data, FieldReference.from(reference));
     }
 }
diff --git a/logstash-core/src/test/java/org/logstash/FieldReferenceTest.java b/logstash-core/src/test/java/org/logstash/FieldReferenceTest.java
index cd757efda..63fd16f67 100644
--- a/logstash-core/src/test/java/org/logstash/FieldReferenceTest.java
+++ b/logstash-core/src/test/java/org/logstash/FieldReferenceTest.java
@@ -51,7 +51,7 @@ public final class FieldReferenceTest {
         final FieldReference emptyReference = FieldReference.from("");
         assertNotNull(emptyReference);
         assertEquals(
-            emptyReference, FieldReference.from(RubyUtil.RUBY.newString("").getByteList())
+            emptyReference, FieldReference.from(RubyUtil.RUBY.newString(""))
         );
     }
 
diff --git a/logstash-core/src/test/java/org/logstash/ext/JrubyEventExtLibraryTest.java b/logstash-core/src/test/java/org/logstash/ext/JrubyEventExtLibraryTest.java
index e531582f7..8cd1e5327 100644
--- a/logstash-core/src/test/java/org/logstash/ext/JrubyEventExtLibraryTest.java
+++ b/logstash-core/src/test/java/org/logstash/ext/JrubyEventExtLibraryTest.java
@@ -43,6 +43,18 @@ public final class JrubyEventExtLibraryTest {
         }
     }
 
+    @Test
+    public void correctlyHandlesNonAsciiKeys() {
+        final RubyString key = rubyString("[テストフィールド]");
+        final RubyString value = rubyString("someValue");
+        final ThreadContext context = RubyUtil.RUBY.getCurrentContext();
+        final JrubyEventExtLibrary.RubyEvent event =
+            JrubyEventExtLibrary.RubyEvent.newRubyEvent(context.runtime);
+        event.ruby_set_field(context, key, value);
+        Assertions.assertThat(event.ruby_to_json(context, new IRubyObject[0]).asJavaString())
+            .contains("\"テストフィールド\":\"someValue\"");
+    }
+
     private static RubyString rubyString(final String java) {
         return RubyUtil.RUBY.newString(java);
     }