diff --git a/src/main/java/org/apache/commons/text/similarity/LongestCommonSubsequence.java b/src/main/java/org/apache/commons/text/similarity/LongestCommonSubsequence.java
index 86bc097ea5..a200bf6cd1 100644
--- a/src/main/java/org/apache/commons/text/similarity/LongestCommonSubsequence.java
+++ b/src/main/java/org/apache/commons/text/similarity/LongestCommonSubsequence.java
@@ -284,12 +284,16 @@ public CharSequence longestCommonSubsequence(final CharSequence left, final Char
      * @param left first character sequence.
      * @param right second character sequence.
      * @return longest common substring length array.
+     * @throws IllegalArgumentException if either String input {@code null}.
      * @deprecated Deprecated as of 1.10. A more efficient implementation for calculating LCS is now available.
      * Use {@link #longestCommonSubsequence(CharSequence, CharSequence)} instead to directly calculate the LCS.
      * This method will be removed in 2.0.
      */
     @Deprecated
     public int[][] longestCommonSubstringLengthArray(final CharSequence left, final CharSequence right) {
+        if (left == null || right == null) {
+            throw new IllegalArgumentException("Inputs must not be null");
+        }
         final int[][] lcsLengthArray = new int[left.length() + 1][right.length() + 1];
         for (int i = 0; i < left.length(); i++) {
             for (int j = 0; j < right.length(); j++) {
diff --git a/src/test/java/org/apache/commons/text/similarity/LongestCommonSubsequenceTest.java b/src/test/java/org/apache/commons/text/similarity/LongestCommonSubsequenceTest.java
index f7d64874de..839488caea 100644
--- a/src/test/java/org/apache/commons/text/similarity/LongestCommonSubsequenceTest.java
+++ b/src/test/java/org/apache/commons/text/similarity/LongestCommonSubsequenceTest.java
@@ -68,6 +68,24 @@ void testGettingLongestCommonSubsequenceApplyStringNull() {
         assertThrows(IllegalArgumentException.class, () -> subject.apply(" ", null));
     }
 
+    @Test
+    @SuppressWarnings("deprecation")
+    void testGettingLongestCommonSubstringLengthArrayNullNull() {
+        assertThrows(IllegalArgumentException.class, () -> subject.longestCommonSubstringLengthArray(null, null));
+    }
+
+    @Test
+    @SuppressWarnings("deprecation")
+    void testGettingLongestCommonSubstringLengthArrayNullString() {
+        assertThrows(IllegalArgumentException.class, () -> subject.longestCommonSubstringLengthArray(null, "right"));
+    }
+
+    @Test
+    @SuppressWarnings("deprecation")
+    void testGettingLongestCommonSubstringLengthArrayStringNull() {
+        assertThrows(IllegalArgumentException.class, () -> subject.longestCommonSubstringLengthArray(" ", null));
+    }
+
     @Test
     void testGettingLongestCommonSubsequenceNullNull() {
         assertThrows(IllegalArgumentException.class, () -> subject.longestCommonSubsequence(null, null));