diff --git a/lucene/CHANGES.txt b/lucene/CHANGES.txt
index dd7c4d07db4..e3376fdb07c 100644
--- a/lucene/CHANGES.txt
+++ b/lucene/CHANGES.txt
@@ -242,6 +242,8 @@ Optimizations
 * GITHUB#12702: Disable suffix sharing for block tree index, making writing the terms dictionary index faster
   and less RAM hungry, while making the index a bit (~1.X% for the terms index file on wikipedia). (Guo Feng, Mike McCandless)
 
+* GITHUB#12726: Return the same input vector if its a unit vector in VectorUtil#l2normalize. (Shubham Chaudhary)
+
 Changes in runtime behavior
 ---------------------
 
diff --git a/lucene/core/src/java/org/apache/lucene/util/VectorUtil.java b/lucene/core/src/java/org/apache/lucene/util/VectorUtil.java
index a978e2d1f1f..ef52e605dbc 100644
--- a/lucene/core/src/java/org/apache/lucene/util/VectorUtil.java
+++ b/lucene/core/src/java/org/apache/lucene/util/VectorUtil.java
@@ -106,18 +106,21 @@ public final class VectorUtil {
    * @throws IllegalArgumentException when the vector is all zero and throwOnZero is true
    */
   public static float[] l2normalize(float[] v, boolean throwOnZero) {
-    double squareSum = IMPL.dotProduct(v, v);
-    int dim = v.length;
-    if (squareSum == 0) {
+    double l1norm = IMPL.dotProduct(v, v);
+    if (l1norm == 0) {
       if (throwOnZero) {
         throw new IllegalArgumentException("Cannot normalize a zero-length vector");
       } else {
         return v;
       }
     }
-    double length = Math.sqrt(squareSum);
+    if (Math.abs(l1norm - 1.0d) <= 1e-5) {
+      return v;
+    }
+    int dim = v.length;
+    double l2norm = Math.sqrt(l1norm);
     for (int i = 0; i < dim; i++) {
-      v[i] /= length;
+      v[i] /= (float) l2norm;
     }
     return v;
   }