diff --git a/extensions/src/main/scala/ai/h2o/sparkling/extensions/rest/api/ImportFrameHandler.scala b/extensions/src/main/scala/ai/h2o/sparkling/extensions/rest/api/ImportFrameHandler.scala
index 6ca178981f..8cd113b394 100644
--- a/extensions/src/main/scala/ai/h2o/sparkling/extensions/rest/api/ImportFrameHandler.scala
+++ b/extensions/src/main/scala/ai/h2o/sparkling/extensions/rest/api/ImportFrameHandler.scala
@@ -96,10 +96,9 @@ class ImportFrameHandler extends Handler {
   private def convertCategoricalColumnsToOtherTypesIfNeeded(frame: Frame, categoricalColumnIndices: Array[Int]) = {
     categoricalColumnIndices.foreach { idx =>
       val vector = frame.vec(idx)
-      val previewWriter =
-        new CategoricalPreviewParseWriter(vector.domain(), vector.length().toInt, vector.naCnt().toInt)
-      val types = previewWriter.guessTypes()
-      types(0) match {
+      val correctType =
+        CategoricalPreviewParseWriter.guessType(vector.domain(), vector.length().toInt, vector.naCnt().toInt)
+      correctType match {
         case Vec.T_CAT => // No action needed
         case Vec.T_STR =>
           Log.info(s"The categorical column '${frame.names()(idx)}' has been converted to string.")
diff --git a/extensions/src/main/scala/water/parser/CategoricalPreviewParseWriter.java b/extensions/src/main/scala/water/parser/CategoricalPreviewParseWriter.java
index 29e91ccba5..bcec218854 100644
--- a/extensions/src/main/scala/water/parser/CategoricalPreviewParseWriter.java
+++ b/extensions/src/main/scala/water/parser/CategoricalPreviewParseWriter.java
@@ -17,29 +17,30 @@
 
 package water.parser;
 
-import java.lang.reflect.Field;
-import water.util.IcedHashMap;
+public class CategoricalPreviewParseWriter {
 
-public class CategoricalPreviewParseWriter extends PreviewParseWriter {
+  public static byte guessType(String[] domain, int nLines, int nEmpty) {
+    final int nStrings = nLines - nEmpty;
+    final int nNums = 0;
+    final int nDates = 0;
+    final int nUUID = 0;
+    final int nZeros = 0;
 
-  public CategoricalPreviewParseWriter(String[] domain, int totalCount, int naCount) {
-    super(1);
-    this._nlines = totalCount;
-    this._nempty[0] = naCount;
-    this._nstrings[0] = totalCount - naCount;
-    IcedHashMap<String, String>[] domains = new IcedHashMap[1];
-    domains[0] = new IcedHashMapWrapper(domain);
-    setPrivateDomains(domains);
-  }
+    PreviewParseWriter.IDomain domainWrapper =
+        new PreviewParseWriter.IDomain() {
+          public int size() {
+            return domain.length;
+          }
+
+          public boolean contains(String value) {
+            for (String domainValue : domain) {
+              if (value.equals(domainValue)) return true;
+            }
+            return false;
+          }
+        };
 
-  private void setPrivateDomains(IcedHashMap<String, String>[] domains) {
-    try {
-      Field domainsField = PreviewParseWriter.class.getDeclaredField("_domains");
-      domainsField.setAccessible(true);
-      domainsField.set(this, domains);
-      domainsField.setAccessible(false);
-    } catch (Exception e) {
-      throw new RuntimeException(e);
-    }
+    return PreviewParseWriter.guessType(
+        nLines, nNums, nStrings, nDates, nUUID, nZeros, nEmpty, domainWrapper);
   }
 }
diff --git a/extensions/src/main/scala/water/parser/IcedHashMapWrapper.java b/extensions/src/main/scala/water/parser/IcedHashMapWrapper.java
deleted file mode 100644
index ed8fff2002..0000000000
--- a/extensions/src/main/scala/water/parser/IcedHashMapWrapper.java
+++ /dev/null
@@ -1,41 +0,0 @@
-/*
- * Licensed to the Apache Software Foundation (ASF) under one or more
- * contributor license agreements.  See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * The ASF licenses this file to You under the Apache License, Version 2.0
- * (the "License"); you may not use this file except in compliance with
- * the License.  You may obtain a copy of the License at
- *
- *    http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package water.parser;
-
-import water.util.IcedHashMap;
-
-public class IcedHashMapWrapper extends IcedHashMap<String, String> {
-  private String[] _values = null;
-
-  public IcedHashMapWrapper(String[] values) {
-    this._values = values;
-  }
-
-  @Override
-  public int size() {
-    return _values.length;
-  }
-
-  @Override
-  public boolean containsKey(Object key) {
-    for (String value : this._values) {
-      if (value.equals(key)) return true;
-    }
-    return false;
-  }
-}
diff --git a/extensions/src/test/scala/water/parser/CategoricalPreviewParseWriterTestSuite.scala b/extensions/src/test/scala/water/parser/CategoricalPreviewParseWriterTestSuite.scala
index 21b7214817..5982dfe542 100644
--- a/extensions/src/test/scala/water/parser/CategoricalPreviewParseWriterTestSuite.scala
+++ b/extensions/src/test/scala/water/parser/CategoricalPreviewParseWriterTestSuite.scala
@@ -46,8 +46,7 @@ class CategoricalPreviewParseWriterTestSuite extends FunSuite with Matchers {
 
       val domain = testCase.filter(_ != null).distinct.toArray
       val naCount = testCase.filter(_ == null).length
-      val categoricalWriter = new CategoricalPreviewParseWriter(domain, testCase.length, naCount)
-      val result = categoricalWriter.guessTypes()(0)
+      val result = CategoricalPreviewParseWriter.guessType(domain, testCase.length, naCount)
 
       result shouldEqual expected
     }