diff --git a/src/jdk.jshell/share/classes/jdk/jshell/execution/impl/ConsoleImpl.java b/src/jdk.jshell/share/classes/jdk/jshell/execution/impl/ConsoleImpl.java
index a697a37141ed8..24de2af52f518 100644
--- a/src/jdk.jshell/share/classes/jdk/jshell/execution/impl/ConsoleImpl.java
+++ b/src/jdk.jshell/share/classes/jdk/jshell/execution/impl/ConsoleImpl.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2023, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -395,7 +395,9 @@ public synchronized void write(int b) throws IOException {
                 buffer = Arrays.copyOf(buffer, 2 * buffer.length);
             }
 
-            buffer[bp++] = b;
+            // Can be negative because widening from byte in write(byte[], int, int).
+            // java.io.OutputStream.write(int b) stipulates "The 24 high-order bits of b are ignored."
+            buffer[bp++] = b & 0xff;
 
             switch (Task.values()[buffer[0]]) {
                 case WRITE_CHARS -> {
@@ -412,7 +414,7 @@ public synchronized void write(int b) throws IOException {
                 }
                 case READ_CHARS -> {
                     if (bp >= 5) {
-                        int len = readInt(b);
+                        int len = readInt(1);
                         int c = console.reader().read();
                         //XXX: EOF handling!
                         sendChars(sinkOutput, new char[] {(char) c}, 0, 1);
diff --git a/test/langtools/jdk/jshell/ConsoleTest.java b/test/langtools/jdk/jshell/ConsoleTest.java
index 4aedc0619397f..7543453684152 100644
--- a/test/langtools/jdk/jshell/ConsoleTest.java
+++ b/test/langtools/jdk/jshell/ConsoleTest.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2023, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -157,6 +157,31 @@ public void close() throws IOException {}
         assertEquals(sb.toString(), expected);
     }
 
+    @Test
+    public void testConsoleUnicodeWritingTest() {
+        StringBuilder sb = new StringBuilder();
+        console = new ThrowingJShellConsole() {
+            @Override
+            public PrintWriter writer() {
+                return new PrintWriter(new Writer() {
+                    @Override
+                    public void write(char[] cbuf, int off, int len) throws IOException {
+                        sb.append(cbuf, off, len);
+                    }
+                    @Override
+                    public void flush() throws IOException {}
+                    @Override
+                    public void close() throws IOException {}
+                });
+            }
+        };
+        int count = 384; // 128-255, 384-511, 640-767, ... (JDK-8355371)
+        String testStr = "\u30A2"; // Japanese katakana (A2 >= 80) (JDK-8354910)
+        assertEval("System.console().writer().write(\"" + testStr + "\".repeat(" + count + "))");
+        String expected = testStr.repeat(count);
+        assertEquals(sb.toString(), expected);
+    }
+
     @Test
     public void testConsoleMultiThreading() {
         StringBuilder sb = new StringBuilder();