diff --git a/core/src/main/java/org/elasticsearch/cluster/metadata/MetaDataIndexUpgradeService.java b/core/src/main/java/org/elasticsearch/cluster/metadata/MetaDataIndexUpgradeService.java
index 2d26ebfd941..bc033fcd6d6 100644
--- a/core/src/main/java/org/elasticsearch/cluster/metadata/MetaDataIndexUpgradeService.java
+++ b/core/src/main/java/org/elasticsearch/cluster/metadata/MetaDataIndexUpgradeService.java
@@ -26,7 +26,6 @@ import org.elasticsearch.cluster.routing.DjbHashFunction;
 import org.elasticsearch.cluster.routing.HashFunction;
 import org.elasticsearch.cluster.routing.SimpleHashFunction;
 import org.elasticsearch.cluster.routing.UnassignedInfo;
-import org.elasticsearch.common.Classes;
 import org.elasticsearch.common.component.AbstractComponent;
 import org.elasticsearch.common.inject.Inject;
 import org.elasticsearch.common.settings.Settings;
@@ -219,7 +218,6 @@ public class MetaDataIndexUpgradeService extends AbstractComponent {
 
     /** All known byte-sized settings for an index. */
     public static final Set<String> INDEX_BYTES_SIZE_SETTINGS = ImmutableSet.of(
-                                    "index.buffer_size",
                                     "index.merge.policy.floor_segment",
                                     "index.merge.policy.max_merged_segment",
                                     "index.merge.policy.max_merge_size",
diff --git a/core/src/main/java/org/elasticsearch/index/engine/EngineConfig.java b/core/src/main/java/org/elasticsearch/index/engine/EngineConfig.java
index 899fa5f162a..d18097953aa 100644
--- a/core/src/main/java/org/elasticsearch/index/engine/EngineConfig.java
+++ b/core/src/main/java/org/elasticsearch/index/engine/EngineConfig.java
@@ -93,15 +93,6 @@ public final class EngineConfig {
      */
     public static final String INDEX_GC_DELETES_SETTING = "index.gc_deletes";
 
-    /**
-     * Index setting to control the initial index buffer size.  NOTE: this setting is somewhat
-     * useless, since IndexingMemoryController will take over quickly and partition the
-     * indices.memory.index_buffer_size for this node across all shards.
-     *
-     * <p>This setting is <b>not</b> realtime updateable.
-     */
-    public static final String INDEX_BUFFER_SIZE_SETTING = "index.buffer_size";
-
     /**
      * Index setting to change the low level lucene codec used for writing new segments.
      * This setting is <b>not</b> realtime updateable.
@@ -155,7 +146,7 @@ public final class EngineConfig {
         this.optimizeAutoGenerateId = indexSettings.getAsBoolean(EngineConfig.INDEX_OPTIMIZE_AUTOGENERATED_ID_SETTING, false);
         this.compoundOnFlush = indexSettings.getAsBoolean(EngineConfig.INDEX_COMPOUND_ON_FLUSH, compoundOnFlush);
         codecName = indexSettings.get(EngineConfig.INDEX_CODEC_SETTING, EngineConfig.DEFAULT_CODEC_NAME);
-        indexingBufferSize = indexSettings.getAsBytesSize(INDEX_BUFFER_SIZE_SETTING, DEFAULT_INDEX_BUFFER_SIZE);
+        indexingBufferSize = DEFAULT_INDEX_BUFFER_SIZE;
         gcDeletesInMillis = indexSettings.getAsTime(INDEX_GC_DELETES_SETTING, EngineConfig.DEFAULT_GC_DELETES).millis();
         versionMapSizeSetting = indexSettings.get(INDEX_VERSION_MAP_SIZE, DEFAULT_VERSION_MAP_SIZE);
         updateVersionMapSize();
@@ -170,7 +161,7 @@ public final class EngineConfig {
     private void updateVersionMapSize() {
         if (versionMapSizeSetting.endsWith("%")) {
             double percent = Double.parseDouble(versionMapSizeSetting.substring(0, versionMapSizeSetting.length() - 1));
-            versionMapSize = new ByteSizeValue((long) (((double) indexingBufferSize.bytes() * (percent / 100))));
+            versionMapSize = new ByteSizeValue((long) ((double) indexingBufferSize.bytes() * (percent / 100)));
         } else {
             versionMapSize = ByteSizeValue.parseBytesSizeValue(versionMapSizeSetting, INDEX_VERSION_MAP_SIZE);
         }
diff --git a/core/src/test/java/org/elasticsearch/index/engine/InternalEngineTests.java b/core/src/test/java/org/elasticsearch/index/engine/InternalEngineTests.java
index 2a76a054973..3381102a419 100644
--- a/core/src/test/java/org/elasticsearch/index/engine/InternalEngineTests.java
+++ b/core/src/test/java/org/elasticsearch/index/engine/InternalEngineTests.java
@@ -20,6 +20,7 @@
 package org.elasticsearch.index.engine;
 
 import com.google.common.collect.ImmutableMap;
+
 import org.apache.log4j.AppenderSkeleton;
 import org.apache.log4j.Level;
 import org.apache.log4j.LogManager;
@@ -52,6 +53,8 @@ import org.elasticsearch.common.logging.ESLogger;
 import org.elasticsearch.common.lucene.Lucene;
 import org.elasticsearch.common.lucene.uid.Versions;
 import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.unit.ByteSizeUnit;
+import org.elasticsearch.common.unit.ByteSizeValue;
 import org.elasticsearch.common.util.BigArrays;
 import org.elasticsearch.index.Index;
 import org.elasticsearch.index.VersionType;
@@ -1637,12 +1640,10 @@ public class InternalEngineTests extends ESTestCase {
     // #10312
     @Test
     public void testDeletesAloneCanTriggerRefresh() throws Exception {
-        // Tiny indexing buffer:
-        Settings indexSettings = Settings.builder().put(defaultSettings)
-                .put(EngineConfig.INDEX_BUFFER_SIZE_SETTING, "1kb").build();
         try (Store store = createStore();
-             Engine engine = new InternalEngine(config(indexSettings, store, createTempDir(), new MergeSchedulerConfig(defaultSettings), newMergePolicy()),
+            Engine engine = new InternalEngine(config(defaultSettings, store, createTempDir(), new MergeSchedulerConfig(defaultSettings), newMergePolicy()),
                      false)) {
+            engine.config().setIndexingBufferSize(new ByteSizeValue(1, ByteSizeUnit.KB));
             for (int i = 0; i < 100; i++) {
                 String id = Integer.toString(i);
                 ParsedDocument doc = testParsedDocument(id, id, "test", null, -1, -1, testDocument(), B_1, null);