diff --git a/core/src/main/java/org/elasticsearch/cluster/ClusterModule.java b/core/src/main/java/org/elasticsearch/cluster/ClusterModule.java
index 7a4a3e0722d..20333e94ee1 100644
--- a/core/src/main/java/org/elasticsearch/cluster/ClusterModule.java
+++ b/core/src/main/java/org/elasticsearch/cluster/ClusterModule.java
@@ -168,7 +168,7 @@ public class ClusterModule extends AbstractModule {
         registerClusterDynamicSetting(IndicesTTLService.INDICES_TTL_INTERVAL, Validator.TIME);
         registerClusterDynamicSetting(MappingUpdatedAction.INDICES_MAPPING_DYNAMIC_TIMEOUT, Validator.TIME);
         registerClusterDynamicSetting(MetaData.SETTING_READ_ONLY, Validator.EMPTY);
-        registerClusterDynamicSetting(RecoverySettings.INDICES_RECOVERY_FILE_CHUNK_SIZE, Validator.BYTES_SIZE);
+        registerClusterDynamicSetting(RecoverySettings.INDICES_RECOVERY_FILE_CHUNK_SIZE, Validator.POSITIVE_BYTES_SIZE);
         registerClusterDynamicSetting(RecoverySettings.INDICES_RECOVERY_TRANSLOG_OPS, Validator.INTEGER);
         registerClusterDynamicSetting(RecoverySettings.INDICES_RECOVERY_TRANSLOG_SIZE, Validator.BYTES_SIZE);
         registerClusterDynamicSetting(RecoverySettings.INDICES_RECOVERY_COMPRESS, Validator.EMPTY);
diff --git a/core/src/main/java/org/elasticsearch/cluster/settings/Validator.java b/core/src/main/java/org/elasticsearch/cluster/settings/Validator.java
index 12049abed9b..cb253dceadf 100644
--- a/core/src/main/java/org/elasticsearch/cluster/settings/Validator.java
+++ b/core/src/main/java/org/elasticsearch/cluster/settings/Validator.java
@@ -22,6 +22,7 @@ package org.elasticsearch.cluster.settings;
 import org.elasticsearch.ElasticsearchParseException;
 import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.common.Booleans;
+import org.elasticsearch.common.unit.ByteSizeValue;
 import org.elasticsearch.common.unit.TimeValue;
 
 import static org.elasticsearch.common.unit.ByteSizeValue.parseBytesSizeValue;
@@ -228,6 +229,21 @@ public interface Validator {
         }
     };
 
+    Validator POSITIVE_BYTES_SIZE = new Validator() {
+        @Override
+        public String validate(String setting, String value, ClusterState state) {
+            try {
+                ByteSizeValue byteSizeValue = parseBytesSizeValue(value, setting);
+                if (byteSizeValue.getBytes() <= 0) {
+                    return setting + " must be a positive byte size value";
+                }
+            } catch (ElasticsearchParseException ex) {
+                return ex.getMessage();
+            }
+            return null;
+        }
+    };
+
     Validator PERCENTAGE = new Validator() {
         @Override
         public String validate(String setting, String value, ClusterState clusterState) {
diff --git a/core/src/main/java/org/elasticsearch/indices/recovery/RecoverySourceHandler.java b/core/src/main/java/org/elasticsearch/indices/recovery/RecoverySourceHandler.java
index 295ab49ac7f..9d0439dc167 100644
--- a/core/src/main/java/org/elasticsearch/indices/recovery/RecoverySourceHandler.java
+++ b/core/src/main/java/org/elasticsearch/indices/recovery/RecoverySourceHandler.java
@@ -293,7 +293,7 @@ public class RecoverySourceHandler {
                             store.incRef();
                             final StoreFileMetaData md = recoverySourceMetadata.get(name);
                             try (final IndexInput indexInput = store.directory().openInput(name, IOContext.READONCE)) {
-                                final int BUFFER_SIZE = (int) recoverySettings.fileChunkSize().bytes();
+                                final int BUFFER_SIZE = (int) Math.max(1, recoverySettings.fileChunkSize().bytes()); // at least one!
                                 final byte[] buf = new byte[BUFFER_SIZE];
                                 boolean shouldCompressRequest = recoverySettings.compress();
                                 if (CompressorFactory.isCompressed(indexInput)) {
diff --git a/core/src/main/java/org/elasticsearch/indices/recovery/RecoveryStatus.java b/core/src/main/java/org/elasticsearch/indices/recovery/RecoveryStatus.java
index b4d5bf6471e..cef24543917 100644
--- a/core/src/main/java/org/elasticsearch/indices/recovery/RecoveryStatus.java
+++ b/core/src/main/java/org/elasticsearch/indices/recovery/RecoveryStatus.java
@@ -226,6 +226,9 @@ public class RecoveryStatus extends AbstractRefCounted {
     public IndexOutput openAndPutIndexOutput(String fileName, StoreFileMetaData metaData, Store store) throws IOException {
         ensureRefCount();
         String tempFileName = getTempNameForFile(fileName);
+        if (tempFileNames.containsKey(tempFileName)) {
+            throw new IllegalStateException("output for file [" + fileName + "] has already been created");
+        }
         // add first, before it's created
         tempFileNames.put(tempFileName, fileName);
         IndexOutput indexOutput = store.createVerifyingOutput(tempFileName, metaData, IOContext.DEFAULT);
diff --git a/core/src/test/java/org/elasticsearch/indices/recovery/RecoveryStatusTests.java b/core/src/test/java/org/elasticsearch/indices/recovery/RecoveryStatusTests.java
index 35847f51ab7..af5c2ef8b09 100644
--- a/core/src/test/java/org/elasticsearch/indices/recovery/RecoveryStatusTests.java
+++ b/core/src/test/java/org/elasticsearch/indices/recovery/RecoveryStatusTests.java
@@ -56,6 +56,13 @@ public class RecoveryStatusTests extends ESSingleNodeTestCase {
             assertSame(openIndexOutput, indexOutput);
             openIndexOutput.writeInt(1);
         }
+        try {
+            status.openAndPutIndexOutput("foo.bar", new StoreFileMetaData("foo.bar", 8), status.store());
+            fail("file foo.bar is already opened and registered");
+        } catch (IllegalStateException ex) {
+            assertEquals("output for file [foo.bar] has already been created", ex.getMessage());
+            // all well = it's already registered
+        }
         status.removeOpenIndexOutputs("foo.bar");
         Set<String> strings = Sets.newHashSet(status.store().directory().listAll());
         String expectedFile = null;
diff --git a/core/src/test/java/org/elasticsearch/recovery/RelocationIT.java b/core/src/test/java/org/elasticsearch/recovery/RelocationIT.java
index c73baac193e..53a71e1dc7b 100644
--- a/core/src/test/java/org/elasticsearch/recovery/RelocationIT.java
+++ b/core/src/test/java/org/elasticsearch/recovery/RelocationIT.java
@@ -402,7 +402,7 @@ public class RelocationIT extends ESIntegTestCase {
 
         // Slow down recovery in order to make recovery cancellations more likely
         IndicesStatsResponse statsResponse = client().admin().indices().prepareStats(indexName).get();
-        long chunkSize = statsResponse.getIndex(indexName).getShards()[0].getStats().getStore().size().bytes() / 10;
+        long chunkSize = Math.max(1, statsResponse.getIndex(indexName).getShards()[0].getStats().getStore().size().bytes() / 10);
         assertTrue(client().admin().cluster().prepareUpdateSettings()
                 .setTransientSettings(Settings.builder()
                                 // one chunk per sec..