diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/return_invalid_type/return_invalid_type.1.ddl.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/return_invalid_type/return_invalid_type.1.ddl.sqlpp
new file mode 100644
index 0000000..e375558
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/return_invalid_type/return_invalid_type.1.ddl.sqlpp
@@ -0,0 +1,63 @@
+/*
+ * 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.
+ */
+
+drop dataverse externallibtest if exists;
+create dataverse externallibtest;
+use externallibtest;
+
+create type TwitterUserType as closed {
+ screen_name: string,
+ language: string,
+ friends_count: int32,
+ status_count: int32,
+ name: string,
+ followers_count: int32
+};
+
+create type Tweet as closed {
+ id: int64,
+ user: TwitterUserType,
+ latitude: double,
+ longitude: double,
+ message_text: string,
+ created_at: string,
+ country: string
+};
+
+create type ProcessedTweet if not exists as open {
+    id: int64,
+    user_name:string,
+    location:point,
+    created_at:string,
+    message_text:string,
+    country: string,
+    topics: {{string}}
+};
+
+create dataset SyntheticTweets(Tweet) primary key id;
+
+create feed  SyntheticTweetFeed using stream
+(("duration"="1"),
+("stream-source"="org.apache.asterix.external.input.stream.factory.TwitterFirehoseStreamFactory"),
+("tps"="50"),
+("type-name"="Tweet"),
+("tput-duration"="1"),
+("dataverse-dataset"="feeds:SyntheticTweets"),
+("format"="adm"),
+("mode"="controlled"));
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/return_invalid_type/return_invalid_type.2.lib.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/return_invalid_type/return_invalid_type.2.lib.sqlpp
new file mode 100644
index 0000000..d1e0e87
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/return_invalid_type/return_invalid_type.2.lib.sqlpp
@@ -0,0 +1,19 @@
+/*
+ * 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.
+ */
+install externallibtest testlib target/data/externallib/asterix-external-data-testlib.zip
\ No newline at end of file
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/return_invalid_type/return_invalid_type.3.update.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/return_invalid_type/return_invalid_type.3.update.sqlpp
new file mode 100644
index 0000000..be057f8
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/return_invalid_type/return_invalid_type.3.update.sqlpp
@@ -0,0 +1,26 @@
+/*
+ * 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.
+ */
+
+use externallibtest;
+
+set `wait-for-completion-feed` `true`;
+
+connect feed SyntheticTweetFeed to dataset SyntheticTweets;
+
+start feed SyntheticTweetFeed;
\ No newline at end of file
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/return_invalid_type/return_invalid_type.4.query.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/return_invalid_type/return_invalid_type.4.query.sqlpp
new file mode 100644
index 0000000..59ea2c4
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/return_invalid_type/return_invalid_type.4.query.sqlpp
@@ -0,0 +1,23 @@
+/*
+ * 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.
+ */
+
+use externallibtest;
+
+SELECT testlib#addHashTagsInPlace(t) FROM SyntheticTweets t;
+
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/testsuite_it_sqlpp.xml b/asterixdb/asterix-app/src/test/resources/runtimets/testsuite_it_sqlpp.xml
index 8f4455f..edba869 100644
--- a/asterixdb/asterix-app/src/test/resources/runtimets/testsuite_it_sqlpp.xml
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/testsuite_it_sqlpp.xml
@@ -48,5 +48,11 @@
         <output-dir compare="Text">feed-with-external-function</output-dir>
       </compilation-unit>
     </test-case>
+    <test-case FilePath="external-library">
+      <compilation-unit name="return_invalid_type">
+        <output-dir compare="Text">getCapital</output-dir>
+        <expected-error>External UDF cannot produce expected result.</expected-error>
+      </compilation-unit>
+    </test-case>
   </test-group>
 </test-suite>
diff --git a/asterixdb/asterix-common/src/main/java/org/apache/asterix/common/exceptions/ErrorCode.java b/asterixdb/asterix-common/src/main/java/org/apache/asterix/common/exceptions/ErrorCode.java
index 279624d..895cd55 100644
--- a/asterixdb/asterix-common/src/main/java/org/apache/asterix/common/exceptions/ErrorCode.java
+++ b/asterixdb/asterix-common/src/main/java/org/apache/asterix/common/exceptions/ErrorCode.java
@@ -74,6 +74,8 @@
 
     public static final int INSTANTIATION_ERROR = 100;
 
+    public static final int EXTERNAL_UDF_RESULT_TYPE_ERROR = 200;
+
     // Compilation errors
     public static final int PARSE_ERROR = 1001;
     public static final int COMPILATION_TYPE_MISMATCH = 1002;
diff --git a/asterixdb/asterix-common/src/main/resources/asx_errormsg/en.properties b/asterixdb/asterix-common/src/main/resources/asx_errormsg/en.properties
index 6ce78f0..98b8e2f 100644
--- a/asterixdb/asterix-common/src/main/resources/asx_errormsg/en.properties
+++ b/asterixdb/asterix-common/src/main/resources/asx_errormsg/en.properties
@@ -67,6 +67,8 @@
 
 100 = Unable to instantiate class %1$s
 
+200 = External UDF cannot produce expected result. Please check the UDF configuration
+
 # Compile-time check errors
 1007 = Invalid expression: function %1$s expects its %2$s input parameter to be a %3$s expression, but the actual expression is %4$s
 1008 = Invalid parameter number: function %1$s cannot take %2$s parameters
diff --git a/asterixdb/asterix-external-data/src/main/java/org/apache/asterix/external/generator/DataGenerator.java b/asterixdb/asterix-external-data/src/main/java/org/apache/asterix/external/generator/DataGenerator.java
index c2eca84..9bc3037 100644
--- a/asterixdb/asterix-external-data/src/main/java/org/apache/asterix/external/generator/DataGenerator.java
+++ b/asterixdb/asterix-external-data/src/main/java/org/apache/asterix/external/generator/DataGenerator.java
@@ -421,7 +421,7 @@
             buffer.append(" ");
             String jargonTerm = jargon.get(random.nextInt(jargon.size()));
             referredTopics.add(jargonTerm);
-            buffer.append(jargonTerm);
+            buffer.append("#" + jargonTerm);
             buffer.append(" is ");
             buffer.append(adjective);
             if (random.nextBoolean()) {
diff --git a/asterixdb/asterix-external-data/src/main/java/org/apache/asterix/external/library/ExternalFunctionProvider.java b/asterixdb/asterix-external-data/src/main/java/org/apache/asterix/external/library/ExternalFunctionProvider.java
index 7602b9a..9e8b9b7 100755
--- a/asterixdb/asterix-external-data/src/main/java/org/apache/asterix/external/library/ExternalFunctionProvider.java
+++ b/asterixdb/asterix-external-data/src/main/java/org/apache/asterix/external/library/ExternalFunctionProvider.java
@@ -25,7 +25,6 @@
 import org.apache.asterix.external.api.IExternalScalarFunction;
 import org.apache.asterix.external.api.IFunctionHelper;
 import org.apache.asterix.om.functions.IExternalFunctionInfo;
-import org.apache.asterix.om.types.ATypeTag;
 import org.apache.hyracks.algebricks.runtime.base.IScalarEvaluator;
 import org.apache.hyracks.algebricks.runtime.base.IScalarEvaluatorFactory;
 import org.apache.hyracks.api.context.IHyracksTaskContext;
@@ -79,14 +78,8 @@
         try {
             resultBuffer.reset();
             ((IExternalScalarFunction) externalFunction).evaluate(argumentProvider);
-            /*
-             * Make sure that if "setResult" is not called,
-             * or the result object is missing we let Hyracks storage manager know
-             * we want to discard a missing object
-             */
-            byte byteOutput = resultBuffer.getByteArray()[0];
-            if (!argumentProvider.isValidResult() || byteOutput == ATypeTag.SERIALIZED_MISSING_TYPE_TAG) {
-                resultBuffer.getDataOutput().writeByte(ATypeTag.SERIALIZED_MISSING_TYPE_TAG);
+            if (!argumentProvider.isValidResult()) {
+                throw new RuntimeDataException(ErrorCode.EXTERNAL_UDF_RESULT_TYPE_ERROR);
             }
         } catch (Exception e) {
             throw new HyracksDataException(e);
diff --git a/asterixdb/asterix-external-data/src/main/java/org/apache/asterix/external/library/JavaFunctionHelper.java b/asterixdb/asterix-external-data/src/main/java/org/apache/asterix/external/library/JavaFunctionHelper.java
index 3006454..a369888 100644
--- a/asterixdb/asterix-external-data/src/main/java/org/apache/asterix/external/library/JavaFunctionHelper.java
+++ b/asterixdb/asterix-external-data/src/main/java/org/apache/asterix/external/library/JavaFunctionHelper.java
@@ -28,6 +28,7 @@
 import org.apache.asterix.external.api.IFunctionHelper;
 import org.apache.asterix.external.api.IJObject;
 import org.apache.asterix.external.library.java.JObjectPointableVisitor;
+import org.apache.asterix.external.library.java.JObjects;
 import org.apache.asterix.external.library.java.JObjects.JNull;
 import org.apache.asterix.external.library.java.JTypeTag;
 import org.apache.asterix.om.functions.IExternalFunctionInfo;
@@ -36,6 +37,7 @@
 import org.apache.asterix.om.pointables.ARecordVisitablePointable;
 import org.apache.asterix.om.pointables.PointableAllocator;
 import org.apache.asterix.om.pointables.base.IVisitablePointable;
+import org.apache.asterix.om.types.ATypeTag;
 import org.apache.asterix.om.types.BuiltinType;
 import org.apache.asterix.om.types.IAType;
 import org.apache.asterix.om.util.container.IObjectPool;
@@ -81,8 +83,7 @@
 
     @Override
     public void setResult(IJObject result) throws HyracksDataException {
-        if (result == null) {
-            JNull.INSTANCE.serialize(outputProvider.getDataOutput(), true);
+        if (result == null || checkInvalidReturnValueType(result, finfo.getReturnType())) {
             isValidResult = false;
         } else {
             isValidResult = true;
@@ -91,6 +92,16 @@
         }
     }
 
+    private boolean checkInvalidReturnValueType(IJObject result, IAType expectedType) {
+        if (expectedType.getTypeTag() != result.getTypeTag()) {
+            return true;
+        }
+        if (expectedType.getTypeTag() == ATypeTag.OBJECT) {
+            return !expectedType.getTypeName().equals(((JObjects.JRecord) result).getRecordType().getTypeName());
+        }
+        return false;
+    }
+
     /**
      * Gets the value of the result flag
      *
diff --git a/asterixdb/asterix-external-data/src/test/java/org/apache/asterix/external/library/AddHashTagsFunction.java b/asterixdb/asterix-external-data/src/test/java/org/apache/asterix/external/library/AddHashTagsFunction.java
index 96a40fb..3c6881a 100644
--- a/asterixdb/asterix-external-data/src/test/java/org/apache/asterix/external/library/AddHashTagsFunction.java
+++ b/asterixdb/asterix-external-data/src/test/java/org/apache/asterix/external/library/AddHashTagsFunction.java
@@ -78,7 +78,6 @@
         outputRecord.setField(Datatypes.Tweet.MESSAGE, text);
         outputRecord.setField(Datatypes.ProcessedTweet.TOPICS, list);
 
-        inputRecord.addField(Datatypes.ProcessedTweet.TOPICS, list);
         functionHelper.setResult(outputRecord);
     }