diff --git a/server/src/main/java/org/opensearch/index/IndexSettings.java b/server/src/main/java/org/opensearch/index/IndexSettings.java
index 8ac024e003f74..ac6ba8d688c45 100644
--- a/server/src/main/java/org/opensearch/index/IndexSettings.java
+++ b/server/src/main/java/org/opensearch/index/IndexSettings.java
@@ -112,7 +112,12 @@ public static IndexMergePolicy fromString(String text) {
                     return policy;
                 }
             }
-            return null;
+            throw new IllegalArgumentException(
+                "The setting has unsupported policy specified: "
+                    + text
+                    + ". Please use one of: "
+                    + String.join(", ", Arrays.stream(IndexMergePolicy.values()).map(IndexMergePolicy::getValue).toArray(String[]::new))
+            );
         }
     }
 
@@ -601,34 +606,17 @@ public static IndexMergePolicy fromString(String text) {
         Property.Dynamic
     );
 
-    public static final Setting<String> INDEX_MERGE_POLICY = Setting.simpleString("index.merge.policy", DEFAULT_POLICY, policy -> {
-        if (IndexMergePolicy.fromString(policy) == null) {
-            throw new IllegalArgumentException(
-                "The "
-                    + IndexSettings.INDEX_MERGE_POLICY.getKey()
-                    + " has unsupported policy specified: "
-                    + policy
-                    + ". Please use one of: "
-                    + String.join(", ", Arrays.stream(IndexMergePolicy.values()).map(IndexMergePolicy::getValue).toArray(String[]::new))
-            );
-        }
-    }, Property.IndexScope);
+    public static final Setting<String> INDEX_MERGE_POLICY = Setting.simpleString(
+        "index.merge.policy",
+        DEFAULT_POLICY,
+        IndexMergePolicy::fromString,
+        Property.IndexScope
+    );
 
     public static final Setting<String> TIME_INDEX_MERGE_POLICY = Setting.simpleString(
         "indices.time_index.default_index_merge_policy",
         DEFAULT_POLICY,
-        policy -> {
-            if (IndexMergePolicy.fromString(policy) == null) {
-                throw new IllegalArgumentException(
-                    "The "
-                        + IndexSettings.TIME_INDEX_MERGE_POLICY.getKey()
-                        + " has unsupported policy specified: "
-                        + policy
-                        + ". Please use one of: "
-                        + String.join(", ", Arrays.stream(IndexMergePolicy.values()).map(IndexMergePolicy::getValue).toArray(String[]::new))
-                );
-            }
-        },
+        IndexMergePolicy::fromString,
         Property.NodeScope
     );
 
diff --git a/server/src/test/java/org/opensearch/index/MergePolicySettingsTests.java b/server/src/test/java/org/opensearch/index/MergePolicySettingsTests.java
index 2b6bff33a18ca..a98c00879fbc1 100644
--- a/server/src/test/java/org/opensearch/index/MergePolicySettingsTests.java
+++ b/server/src/test/java/org/opensearch/index/MergePolicySettingsTests.java
@@ -188,31 +188,25 @@ public void testInvalidMergePolicy() throws IOException {
             IllegalArgumentException.class,
             () -> IndexSettings.INDEX_MERGE_POLICY.get(invalidSettings)
         );
-        assertThat(exc1.getMessage(), containsString(IndexSettings.INDEX_MERGE_POLICY.getKey() + " has unsupported policy specified: "));
+        assertThat(exc1.getMessage(), containsString(" has unsupported policy specified: "));
         IllegalArgumentException exc2 = expectThrows(
             IllegalArgumentException.class,
             () -> indexSettings(invalidSettings).getMergePolicy(false)
         );
-        assertThat(exc2.getMessage(), containsString(IndexSettings.INDEX_MERGE_POLICY.getKey() + " has unsupported policy specified: "));
+        assertThat(exc2.getMessage(), containsString(" has unsupported policy specified: "));
 
         final Settings invalidSettings2 = Settings.builder().put(IndexSettings.TIME_INDEX_MERGE_POLICY.getKey(), "invalid").build();
         IllegalArgumentException exc3 = expectThrows(
             IllegalArgumentException.class,
             () -> IndexSettings.TIME_INDEX_MERGE_POLICY.get(invalidSettings2)
         );
-        assertThat(
-            exc3.getMessage(),
-            containsString(IndexSettings.TIME_INDEX_MERGE_POLICY.getKey() + " has unsupported policy specified: ")
-        );
+        assertThat(exc3.getMessage(), containsString(" has unsupported policy specified: "));
 
         IllegalArgumentException exc4 = expectThrows(
             IllegalArgumentException.class,
             () -> new IndexSettings(newIndexMeta("test", Settings.EMPTY), invalidSettings2).getMergePolicy(true)
         );
-        assertThat(
-            exc4.getMessage(),
-            containsString(IndexSettings.TIME_INDEX_MERGE_POLICY.getKey() + " has unsupported policy specified: ")
-        );
+        assertThat(exc4.getMessage(), containsString(" has unsupported policy specified: "));
     }
 
     public void testUpdateSettingsForLogByteSizeMergePolicy() throws IOException {