diff --git a/x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/security/support/StringMatcherTests.java b/x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/security/support/StringMatcherTests.java
index 4c01d4b540c0e..0bca58b32a93e 100644
--- a/x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/security/support/StringMatcherTests.java
+++ b/x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/security/support/StringMatcherTests.java
@@ -108,8 +108,8 @@ public void testSingleRegex() throws Exception {
 
     public void testMultiplePatterns() throws Exception {
         final String prefix1 = randomAlphaOfLengthBetween(3, 5);
-        final String prefix2 = randomAlphaOfLengthBetween(5, 8);
-        final String prefix3 = randomAlphaOfLengthBetween(10, 12);
+        final String prefix2 = randomValueOtherThanMany(s -> s.startsWith(prefix1), () -> randomAlphaOfLengthBetween(5, 8));
+        final String prefix3 = randomValueOtherThanMany(s -> s.startsWith(prefix1), () -> randomAlphaOfLengthBetween(10, 12));
         final String suffix1 = randomAlphaOfLengthBetween(5, 10);
         final String suffix2 = randomAlphaOfLengthBetween(8, 12);
         final String exact1 = randomValueOtherThanMany(
@@ -129,19 +129,32 @@ public void testMultiplePatterns() throws Exception {
             List.of(prefix1 + "*", prefix2 + "?", "/" + prefix3 + "@/", "*" + suffix1, "/@" + suffix2 + "/", exact1, exact2, exact3)
         );
 
+        final List<Character> nonAlpha = "@/#$0123456789()[]{}<>;:%&".chars()
+            .mapToObj(c -> Character.valueOf((char) c))
+            .collect(Collectors.toList());
+
         assertMatch(matcher, exact1);
         assertMatch(matcher, exact2);
         assertMatch(matcher, exact3);
         assertMatch(matcher, randomAlphaOfLength(3) + suffix1);
         assertMatch(matcher, randomAlphaOfLength(3) + suffix2);
+
+        // Prefix 1 uses '*', it should match any number of trailing chars.
         assertMatch(matcher, prefix1 + randomAlphaOfLengthBetween(1, 5));
-        assertMatch(matcher, prefix2 + randomAlphaOfLength(1));
-        assertMatch(matcher, prefix3 + randomAlphaOfLengthBetween(1, 5));
+        assertMatch(matcher, prefix1 + randomFrom(nonAlpha));
+        assertMatch(matcher, prefix1 + randomFrom(nonAlpha) + randomFrom(nonAlpha));
 
-        final char[] nonAlpha = "@/#$0123456789()[]{}<>;:%&".toCharArray();
+        // Prefix 2 uses a `?`, it should match any single trailing char, but not 2 chars.
+        // (We don't test with a trailing alpha because it might match one of the matched suffixes)
+        assertMatch(matcher, prefix2 + randomAlphaOfLength(1));
+        assertMatch(matcher, prefix2 + randomFrom(nonAlpha));
+        assertNoMatch(matcher, prefix2 + randomFrom(nonAlpha) + randomFrom(nonAlpha));
+        assertNoMatch(matcher, prefix2 + randomAlphaOfLength(1) + randomFrom(nonAlpha));
 
-        // Prefix 2 uses a `?`
-        assertNoMatch(matcher, prefix2 + randomFrom(nonAlpha));
+        // Prefix 3 uses a regex with '@', it should match any number of trailing chars.
+        assertMatch(matcher, prefix3 + randomAlphaOfLengthBetween(1, 5));
+        assertMatch(matcher, prefix3 + randomFrom(nonAlpha));
+        assertMatch(matcher, prefix3 + randomFrom(nonAlpha) + randomFrom(nonAlpha));
 
         for (String pattern : List.of(exact1, exact2, exact3, suffix1, suffix2, exact1, exact2, exact3)) {
             assertNoMatch(matcher, randomFrom(nonAlpha) + pattern + randomFrom(nonAlpha));