diff --git a/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/IntroduceDynamicTypeCastForExternalFunctionRule.java b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/IntroduceDynamicTypeCastForExternalFunctionRule.java
index c9a873b..bb39993 100644
--- a/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/IntroduceDynamicTypeCastForExternalFunctionRule.java
+++ b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/IntroduceDynamicTypeCastForExternalFunctionRule.java
@@ -25,7 +25,6 @@
 import org.apache.asterix.om.typecomputer.base.TypeCastUtils;
 import org.apache.asterix.om.types.ARecordType;
 import org.apache.asterix.om.types.AUnionType;
-import org.apache.asterix.om.types.BuiltinType;
 import org.apache.asterix.om.types.IAType;
 import org.apache.asterix.om.utils.NonTaggedFormatUtil;
 import org.apache.commons.lang3.mutable.Mutable;
@@ -39,7 +38,6 @@
 import org.apache.hyracks.algebricks.core.algebra.expressions.AbstractFunctionCallExpression;
 import org.apache.hyracks.algebricks.core.algebra.expressions.ScalarFunctionCallExpression;
 import org.apache.hyracks.algebricks.core.algebra.operators.logical.AbstractLogicalOperator;
-import org.apache.hyracks.algebricks.core.algebra.operators.logical.AssignOperator;
 import org.apache.hyracks.algebricks.core.rewriter.base.IAlgebraicRewriteRule;
 
 /**
@@ -58,12 +56,21 @@
     private boolean rewriteFunctionArgs(ILogicalOperator op, Mutable<ILogicalExpression> expRef,
             IOptimizationContext context) throws AlgebricksException {
         ILogicalExpression expr = expRef.getValue();
-        if (expr.getExpressionTag() != LogicalExpressionTag.FUNCTION_CALL
-                || !(expr instanceof ScalarFunctionCallExpression)) {
+        if (expr.getExpressionTag() != LogicalExpressionTag.FUNCTION_CALL) {
             return false;
         }
-        ScalarFunctionCallExpression funcCallExpr = (ScalarFunctionCallExpression) expr;
         boolean changed = false;
+        // go over all arguments recursively
+        AbstractFunctionCallExpression funcCallExpr = (AbstractFunctionCallExpression) expr;
+        for (Mutable<ILogicalExpression> functionArgRef : funcCallExpr.getArguments()) {
+            if (rewriteFunctionArgs(op, functionArgRef, context)) {
+                changed = true;
+            }
+        }
+        // if the current function is builtin function, skip the type casting
+        if (BuiltinFunctions.getBuiltinFunctionIdentifier(funcCallExpr.getFunctionIdentifier()) != null) {
+            return changed;
+        }
         IAType inputRecordType;
         ARecordType requiredRecordType;
         for (int iter1 = 0; iter1 < funcCallExpr.getArguments().size(); iter1++) {
@@ -105,19 +112,6 @@
         if (op.getOperatorTag() != LogicalOperatorTag.ASSIGN) {
             return false;
         }
-        AssignOperator assignOp = (AssignOperator) op;
-        ILogicalExpression assignExpr = assignOp.getExpressions().get(0).getValue();
-        if (assignExpr.getExpressionTag() != LogicalExpressionTag.FUNCTION_CALL) {
-            return false;
-        }
-        if (BuiltinFunctions.getBuiltinFunctionIdentifier(
-                ((AbstractFunctionCallExpression) assignExpr).getFunctionIdentifier()) != null) {
-            return false;
-        }
-        if (op.acceptExpressionTransform(exprRef -> rewriteFunctionArgs(op, exprRef, context))) {
-            return true;
-        } else {
-            return false;
-        }
+        return op.acceptExpressionTransform(expr -> rewriteFunctionArgs(op, expr, context));
     }
 }
diff --git a/asterixdb/asterix-app/src/test/java/org/apache/asterix/test/common/ResultExtractor.java b/asterixdb/asterix-app/src/test/java/org/apache/asterix/test/common/ResultExtractor.java
index 0bba635..8c0f8e1 100644
--- a/asterixdb/asterix-app/src/test/java/org/apache/asterix/test/common/ResultExtractor.java
+++ b/asterixdb/asterix-app/src/test/java/org/apache/asterix/test/common/ResultExtractor.java
@@ -52,11 +52,13 @@
 
         String type = "";
         String status = "";
-        String results = "";
+        StringBuilder resultBuilder = new StringBuilder();
         String field = "";
+        String fieldPrefix = "";
         for (Iterator<String> sIter = result.fieldNames(); sIter.hasNext();) {
             field = sIter.next();
-            switch (field) {
+            fieldPrefix = field.split("-")[0];
+            switch (fieldPrefix) {
                 case "requestID":
                     break;
                 case "clientContextID":
@@ -81,32 +83,30 @@
                 case "results":
                     if (result.get(field).size() <= 1) {
                         if (result.get(field).size() == 0) {
-                            results = "";
+                            resultBuilder.append("");
                         } else if (result.get(field).isArray()) {
                             if (result.get(field).get(0).isTextual()) {
-                                results = result.get(field).get(0).asText();
+                                resultBuilder.append(result.get(field).get(0).asText());
                             } else {
                                 ObjectMapper omm = new ObjectMapper();
                                 omm.setDefaultPrettyPrinter(singleLine);
                                 omm.enable(SerializationFeature.INDENT_OUTPUT);
-                                results = omm.writer(singleLine).writeValueAsString(result.get(field));
+                                resultBuilder.append(omm.writer(singleLine).writeValueAsString(result.get(field)));
                             }
                         } else {
-                            results = om.writeValueAsString(result.get(field));
+                            resultBuilder.append(om.writeValueAsString(result.get(field)));
                         }
                     } else {
-                        StringBuilder sb = new StringBuilder();
                         JsonNode[] fields = Iterators.toArray(result.get(field).elements(), JsonNode.class);
                         if (fields.length > 1) {
                             for (JsonNode f : fields) {
                                 if (f.isObject()) {
-                                    sb.append(om.writeValueAsString(f));
+                                    resultBuilder.append(om.writeValueAsString(f));
                                 } else {
-                                    sb.append(f.asText());
+                                    resultBuilder.append(f.asText());
                                 }
                             }
                         }
-                        results = sb.toString();
                     }
                     break;
                 default:
@@ -114,7 +114,7 @@
             }
         }
 
-        return IOUtils.toInputStream(results);
+        return IOUtils.toInputStream(resultBuilder.toString());
     }
 
     public static String extractHandle(InputStream resultStream) throws Exception {
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries/external-library/upperCase/upperCase.3.query.aql b/asterixdb/asterix-app/src/test/resources/runtimets/queries/external-library/upperCase/upperCase.3.query.aql
index 61ed394..5f0b86c 100644
--- a/asterixdb/asterix-app/src/test/resources/runtimets/queries/external-library/upperCase/upperCase.3.query.aql
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries/external-library/upperCase/upperCase.3.query.aql
@@ -23,3 +23,6 @@
 
 let $i:=testlib#toUpper({"id":1, "text":"lower text"})
 return $i;
+
+let $i:= {"field1" : testlib#toUpper({"id":1, "text":"lower text"}), "field2": 123}
+return $i;
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/upperCase/upperCase.1.ddl.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/upperCase/upperCase.1.ddl.sqlpp
new file mode 100644
index 0000000..8130de2
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/upperCase/upperCase.1.ddl.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.
+ */
+DROP DATAVERSE externallibtest if exists;
+CREATE DATAVERSE  externallibtest;
+USE externallibtest;
+
+create type TextType if not exists as open {
+    id: int32,
+    text: string
+};
\ No newline at end of file
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/upperCase/upperCase.2.lib.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/upperCase/upperCase.2.lib.sqlpp
new file mode 100644
index 0000000..d1e0e87
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/upperCase/upperCase.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/upperCase/upperCase.3.query.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/upperCase/upperCase.3.query.sqlpp
new file mode 100644
index 0000000..f361232
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/upperCase/upperCase.3.query.sqlpp
@@ -0,0 +1,28 @@
+/*
+ * 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;
+
+let i={"id":1, "text":"lower text"}
+select value `testlib#toUpper`(i);
+
+let i=`testlib#toUpper`({"id":1, "text":"lower text"})
+select value i;
+
+let i= {"field1" : `testlib#toUpper`({"id":1, "text":"lower text"}), "field2": 123}
+select value i;
\ No newline at end of file
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/upperCase/upperCase.4.lib.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/upperCase/upperCase.4.lib.sqlpp
new file mode 100644
index 0000000..86af80f
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/upperCase/upperCase.4.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.
+ */
+uninstall externallibtest testlib
\ No newline at end of file
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/string/uppercase/uppercase.3.query.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/string/uppercase/uppercase.3.query.sqlpp
index cf01d92..bd15944 100644
--- a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/string/uppercase/uppercase.3.query.sqlpp
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/string/uppercase/uppercase.3.query.sqlpp
@@ -19,5 +19,4 @@
 
 use test;
 
-
 {'result1':test.uppercase('Hellow'),'result2':test.uppercase(''),'result3':test.uppercase(null)};
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/upperCase/upperCase.1.adm b/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/upperCase/upperCase.1.adm
index f475435..e4af2be 100644
--- a/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/upperCase/upperCase.1.adm
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/upperCase/upperCase.1.adm
@@ -1,2 +1,3 @@
 { "id": -1, "text": "LOWER TEXT" }
-{ "id": -1, "text": "LOWER TEXT" }
\ No newline at end of file
+{ "id": -1, "text": "LOWER TEXT" }
+{ "field1": { "id": -1, "text": "LOWER TEXT" }, "field2": 123 }
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 4502a85..83cdd82 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
@@ -38,5 +38,10 @@
         <output-dir compare="Text">getCapital</output-dir>
       </compilation-unit>
     </test-case>
+    <test-case FilePath="external-library">
+      <compilation-unit name="upperCase">
+        <output-dir compare="Text">upperCase</output-dir>
+      </compilation-unit>
+    </test-case>
   </test-group>
 </test-suite>