diff --git a/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HStore.java b/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HStore.java
index 5216fe6b42b..61f5cea361e 100644
--- a/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HStore.java
+++ b/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HStore.java
@@ -299,7 +299,10 @@ public class HStore implements Store, HeapSize, StoreConfigInformation, Propagat
     }
 
     this.storeEngine = createStoreEngine(this, this.conf, this.comparator);
-    this.storeEngine.getStoreFileManager().loadFiles(loadStoreFiles());
+    List<HStoreFile> hStoreFiles = loadStoreFiles();
+    this.storeSize.addAndGet(getStorefilesSize(hStoreFiles, sf -> true));
+    this.totalUncompressedBytes.addAndGet(getTotalUmcompressedBytes(hStoreFiles));
+    this.storeEngine.getStoreFileManager().loadFiles(hStoreFiles);
 
     // Initialize checksum type from name. The names are CRC32, CRC32C, etc.
     this.checksumType = getChecksumType(conf);
@@ -573,10 +576,6 @@ public class HStore implements Store, HeapSize, StoreConfigInformation, Propagat
         try {
           HStoreFile storeFile = completionService.take().get();
           if (storeFile != null) {
-            long length = storeFile.getReader().length();
-            this.storeSize.addAndGet(length);
-            this.totalUncompressedBytes
-                .addAndGet(storeFile.getReader().getTotalUncompressedBytes());
             LOG.debug("loaded {}", storeFile);
             results.add(storeFile);
           }
@@ -2116,24 +2115,24 @@ public class HStore implements Store, HeapSize, StoreConfigInformation, Propagat
   @Override
   public long getStorefilesSize() {
     // Include all StoreFiles
-    return getStorefilesSize(storeFile -> true);
+    return getStorefilesSize(this.storeEngine.getStoreFileManager().getStorefiles(), sf -> true);
   }
 
   @Override
   public long getHFilesSize() {
     // Include only StoreFiles which are HFiles
-    return getStorefilesSize(storeFile -> storeFile.isHFile());
+    return getStorefilesSize(this.storeEngine.getStoreFileManager().getStorefiles(),
+      HStoreFile::isHFile);
   }
 
-  private long getStorefilesSize(Predicate<HStoreFile> predicate) {
-    return this.storeEngine.getStoreFileManager().getStorefiles().stream().filter(sf -> {
-      if (sf.getReader() == null) {
-        LOG.warn("StoreFile {} has a null Reader", sf);
-        return false;
-      } else {
-        return true;
-      }
-    }).filter(predicate).mapToLong(sf -> sf.getReader().length()).sum();
+  private long getTotalUmcompressedBytes(List<HStoreFile> files) {
+    return files.stream().filter(f -> f != null && f.getReader() != null)
+        .mapToLong(f -> f.getReader().getTotalUncompressedBytes()).sum();
+  }
+
+  private long getStorefilesSize(Collection<HStoreFile> files, Predicate<HStoreFile> predicate) {
+    return files.stream().filter(f -> f != null && f.getReader() != null).filter(predicate)
+        .mapToLong(f -> f.getReader().length()).sum();
   }
 
   private long getStoreFileFieldSize(ToLongFunction<StoreFileReader> f) {
diff --git a/hbase-server/src/test/java/org/apache/hadoop/hbase/client/TestAdmin2.java b/hbase-server/src/test/java/org/apache/hadoop/hbase/client/TestAdmin2.java
index 6fc59be2955..4ab1a8fbee0 100644
--- a/hbase-server/src/test/java/org/apache/hadoop/hbase/client/TestAdmin2.java
+++ b/hbase-server/src/test/java/org/apache/hadoop/hbase/client/TestAdmin2.java
@@ -48,10 +48,12 @@ import org.apache.hadoop.hbase.TableNotFoundException;
 import org.apache.hadoop.hbase.UnknownRegionException;
 import org.apache.hadoop.hbase.ZooKeeperConnectionException;
 import org.apache.hadoop.hbase.constraint.ConstraintException;
+import org.apache.hadoop.hbase.ipc.HBaseRpcController;
 import org.apache.hadoop.hbase.master.HMaster;
 import org.apache.hadoop.hbase.master.assignment.AssignmentManager;
 import org.apache.hadoop.hbase.regionserver.HRegion;
 import org.apache.hadoop.hbase.regionserver.HRegionServer;
+import org.apache.hadoop.hbase.regionserver.HStore;
 import org.apache.hadoop.hbase.testclassification.ClientTests;
 import org.apache.hadoop.hbase.testclassification.LargeTests;
 import org.apache.hadoop.hbase.util.Bytes;
@@ -59,6 +61,7 @@ import org.apache.hadoop.hbase.util.Pair;
 import org.apache.hadoop.hbase.wal.AbstractFSWALProvider;
 import org.junit.After;
 import org.junit.AfterClass;
+import org.junit.Assert;
 import org.junit.Before;
 import org.junit.BeforeClass;
 import org.junit.ClassRule;
@@ -754,4 +757,40 @@ public class TestAdmin2 {
       }
     }
   }
+
+  /**
+   * TestCase for HBASE-21355
+   */
+  @Test
+  public void testGetRegionInfo() throws Exception {
+    final TableName tableName = TableName.valueOf(name.getMethodName());
+    Table table = TEST_UTIL.createTable(tableName, Bytes.toBytes("f"));
+    for (int i = 0; i < 100; i++) {
+      table.put(new Put(Bytes.toBytes(i)).addColumn(Bytes.toBytes("f"), Bytes.toBytes("q"),
+        Bytes.toBytes(i)));
+    }
+    admin.flush(tableName);
+
+    HRegionServer rs = TEST_UTIL.getRSForFirstRegionInTable(table.getName());
+    List<HRegion> regions = rs.getRegions(tableName);
+    Assert.assertEquals(1, regions.size());
+
+    HRegion region = regions.get(0);
+    byte[] regionName = region.getRegionInfo().getRegionName();
+    HStore store = region.getStore(Bytes.toBytes("f"));
+    long expectedStoreFilesSize = store.getStorefilesSize();
+    Assert.assertNotNull(store);
+    Assert.assertEquals(expectedStoreFilesSize, store.getSize());
+
+    ClusterConnection conn = ((ClusterConnection) admin.getConnection());
+    HBaseRpcController controller = conn.getRpcControllerFactory().newController();
+    for (int i = 0; i < 10; i++) {
+      RegionInfo ri =
+          ProtobufUtil.getRegionInfo(controller, conn.getAdmin(rs.getServerName()), regionName);
+      Assert.assertEquals(region.getRegionInfo(), ri);
+
+      // Make sure that the store size is still the actual file system's store size.
+      Assert.assertEquals(expectedStoreFilesSize, store.getSize());
+    }
+  }
 }