diff --git a/src/hotspot/cpu/x86/c2_stubGenerator_x86_64_string.cpp b/src/hotspot/cpu/x86/c2_stubGenerator_x86_64_string.cpp
index 0951bda0d17..77a149addb5 100644
--- a/src/hotspot/cpu/x86/c2_stubGenerator_x86_64_string.cpp
+++ b/src/hotspot/cpu/x86/c2_stubGenerator_x86_64_string.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2024, 2025, Intel Corporation. All rights reserved.
+ * Copyright (c) 2024, 2026, Intel Corporation. All rights reserved.
  *
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
@@ -1330,10 +1330,12 @@ static void big_case_loop_helper(bool sizeKnown, int size, Label &noMatch, Label
   // Clarification:  The BYTE_K compare above compares haystack[(n-32):(n-1)].  We need to
   // compare haystack[(k-1):(k-1+31)].  Subtracting either index gives shift value of
   // (k + 31 - n):  x = (k-1+31)-(n-1) = k-1+31-n+1 = k+31-n.
+  // When isU is set, similarly, shift is from haystack[(n-32):(n-1)] to [(k-2):(k-2+31)]
+
   if (sizeKnown) {
-    __ movl(temp2, 31 + size);
+    __ movl(temp2, (isU ? 30 : 31) + size);
   } else {
-    __ movl(temp2, 31);
+    __ movl(temp2, isU ? 30 : 31);
     __ addl(temp2, needleLen);
   }
   __ subl(temp2, hsLength);
diff --git a/test/jdk/java/lang/String/IndexOf.java b/test/jdk/java/lang/String/IndexOf.java
index b4fd17105a8..48f23de79b0 100644
--- a/test/jdk/java/lang/String/IndexOf.java
+++ b/test/jdk/java/lang/String/IndexOf.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2024, Intel Corporation. All rights reserved.
+ * Copyright (c) 2024, 2026, Intel Corporation. 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
@@ -37,6 +37,15 @@
  * @run main/othervm -XX:+IgnoreUnrecognizedVMOptions -Xcomp -XX:-TieredCompilation -XX:UseAVX=2 -XX:+UnlockDiagnosticVMOptions -XX:+EnableX86ECoreOpts IndexOf
  */
 
+/*
+ * @test
+ * @bug 8360271
+ * @summary test String indexOf() intrinsic
+ * @requires vm.cpu.features ~= ".*avx2.*"
+ * @requires vm.compiler2.enabled
+ * @run main/othervm -XX:+IgnoreUnrecognizedVMOptions -Xcomp -XX:-TieredCompilation -XX:UseAVX=2 -XX:+UnlockDiagnosticVMOptions -XX:+EnableX86ECoreOpts -XX:-CompactStrings IndexOf
+ */
+
  public class IndexOf {
   final int scope = 32*2+16+8;
   final char a, aa, b, c, d;
@@ -56,11 +65,11 @@
               d = 'd';
               break;
           case UU:
-              a = '\u0061';
+              a = '\u1061';
               aa = a;
-              b = '\u0062';
+              b = '\u1062';
               c = '\u1063';
-              d = '\u0064';
+              d = '\u1064';
               break;
           default: //case UL:
               a = 'a';
@@ -73,7 +82,7 @@
   }
 
   // needle    =~ /ab*d/
-  // badNeedle =~ /ab*db*d/
+  // badNeedle =~ /ab*cb*d/
   interface Append {void append(int pos, char cc);}
   String newNeedle(int size, int badPosition) {
       if (size<2) {throw new RuntimeException("Fix testcase "+size);}