diff --git a/asterix-app/src/test/resources/runtimets/queries/user-defined-functions/query-issue172/query-issue172.1.ddl.aql b/asterix-app/src/test/resources/runtimets/queries/user-defined-functions/query-issue172/query-issue172.1.ddl.aql
new file mode 100644
index 0000000..e1fab96
--- /dev/null
+++ b/asterix-app/src/test/resources/runtimets/queries/user-defined-functions/query-issue172/query-issue172.1.ddl.aql
@@ -0,0 +1,7 @@
+/*
+ * Description  : This test case is to verify the fix for issue172
+ 				: https://code.google.com/p/asterixdb/issues/detail?id=172
+ * Expected Res : Success
+ * Date         : 19th May 2013
+ */
+ 
diff --git a/asterix-app/src/test/resources/runtimets/queries/user-defined-functions/query-issue172/query-issue172.2.update.aql b/asterix-app/src/test/resources/runtimets/queries/user-defined-functions/query-issue172/query-issue172.2.update.aql
new file mode 100644
index 0000000..b08fc74
--- /dev/null
+++ b/asterix-app/src/test/resources/runtimets/queries/user-defined-functions/query-issue172/query-issue172.2.update.aql
@@ -0,0 +1,7 @@
+/*
+ * Description  : This test case is to verify the fix for issue172
+ 				: https://code.google.com/p/asterixdb/issues/detail?id=172
+ * Expected Res : Success
+ * Date         : 19th May 2013
+ */
+
diff --git a/asterix-app/src/test/resources/runtimets/queries/user-defined-functions/query-issue172/query-issue172.3.query.aql b/asterix-app/src/test/resources/runtimets/queries/user-defined-functions/query-issue172/query-issue172.3.query.aql
new file mode 100644
index 0000000..b695ccb
--- /dev/null
+++ b/asterix-app/src/test/resources/runtimets/queries/user-defined-functions/query-issue172/query-issue172.3.query.aql
@@ -0,0 +1,9 @@
+/*
+ * Description  : This test case is to verify the fix for issue172
+ 				: https://code.google.com/p/asterixdb/issues/detail?id=172
+ * Expected Res : Success
+ * Date         : 19th May 2013
+ */
+
+let $a := string-length(string-concat(["this is a ","test string"]))
+return $a
diff --git a/asterix-app/src/test/resources/runtimets/results/user-defined-functions/query-issue172/query-issue172.1.adm b/asterix-app/src/test/resources/runtimets/results/user-defined-functions/query-issue172/query-issue172.1.adm
new file mode 100644
index 0000000..aabe6ec
--- /dev/null
+++ b/asterix-app/src/test/resources/runtimets/results/user-defined-functions/query-issue172/query-issue172.1.adm
@@ -0,0 +1 @@
+21
diff --git a/asterix-app/src/test/resources/runtimets/testsuite.xml b/asterix-app/src/test/resources/runtimets/testsuite.xml
index 7810a23..f609bf4 100644
--- a/asterix-app/src/test/resources/runtimets/testsuite.xml
+++ b/asterix-app/src/test/resources/runtimets/testsuite.xml
@@ -3953,6 +3953,11 @@
       </compilation-unit>
     </test-case>
     <test-case FilePath="user-defined-functions">
+      <compilation-unit name="query-issue172">
+        <output-dir compare="Text">query-issue172</output-dir>
+      </compilation-unit>
+    </test-case>
+    <test-case FilePath="user-defined-functions">
       <compilation-unit name="query-issue455">
         <output-dir compare="Text">query-issue455</output-dir>
         <expected-error>edu.uci.ics.asterix.common.exceptions.AsterixException</expected-error>
diff --git a/asterix-om/src/main/java/edu/uci/ics/asterix/om/typecomputer/impl/UnaryStringInt32OrNullTypeComputer.java b/asterix-om/src/main/java/edu/uci/ics/asterix/om/typecomputer/impl/UnaryStringInt32OrNullTypeComputer.java
index 2d3018d..7b82c41 100644
--- a/asterix-om/src/main/java/edu/uci/ics/asterix/om/typecomputer/impl/UnaryStringInt32OrNullTypeComputer.java
+++ b/asterix-om/src/main/java/edu/uci/ics/asterix/om/typecomputer/impl/UnaryStringInt32OrNullTypeComputer.java
@@ -1,6 +1,5 @@
 package edu.uci.ics.asterix.om.typecomputer.impl;
 
-
 import java.util.ArrayList;
 import java.util.List;
 
@@ -17,20 +16,21 @@
 import edu.uci.ics.hyracks.algebricks.core.algebra.metadata.IMetadataProvider;
 
 /**
- *
  * @author Xiaoyu Ma
  */
-public class UnaryStringInt32OrNullTypeComputer implements IResultTypeComputer  {   
-    
+public class UnaryStringInt32OrNullTypeComputer implements IResultTypeComputer {
+
     public static final UnaryStringInt32OrNullTypeComputer INSTANCE = new UnaryStringInt32OrNullTypeComputer();
-    private UnaryStringInt32OrNullTypeComputer() {}
-    
+
+    private UnaryStringInt32OrNullTypeComputer() {
+    }
+
     @Override
     public IAType computeType(ILogicalExpression expression, IVariableTypeEnvironment env,
             IMetadataProvider<?, ?> metadataProvider) throws AlgebricksException {
         AbstractFunctionCallExpression fce = (AbstractFunctionCallExpression) expression;
-        if(fce.getArguments().isEmpty())
-            throw new AlgebricksException("Wrong Argument Number.");        
+        if (fce.getArguments().isEmpty())
+            throw new AlgebricksException("Wrong Argument Number.");
         ILogicalExpression arg0 = fce.getArguments().get(0).getValue();
         IAType t0;
         try {
@@ -38,21 +38,23 @@
         } catch (AlgebricksException e) {
             throw new AlgebricksException(e);
         }
-        if (t0.getTypeTag() != ATypeTag.NULL &&
-            t0.getTypeTag() != ATypeTag.STRING ) {
+        if (t0.getTypeTag() != ATypeTag.NULL
+                && t0.getTypeTag() != ATypeTag.STRING
+                && (t0.getTypeTag() == ATypeTag.UNION && !((AUnionType) t0).getUnionList()
+                        .contains(BuiltinType.ASTRING))) {
             throw new NotImplementedException("Expects String Type.");
-        }     
-        
+        }
+
         List<IAType> unionList = new ArrayList<IAType>();
         unionList.add(BuiltinType.ANULL);
-        if(t0.getTypeTag() == ATypeTag.NULL) {
+        if (t0.getTypeTag() == ATypeTag.NULL) { 
             return BuiltinType.ANULL;
         }
-        
-        if(t0.getTypeTag() == ATypeTag.STRING) {
+
+        if (t0.getTypeTag() == ATypeTag.STRING || t0.getTypeTag().equals(ATypeTag.UNION)) {
             unionList.add(BuiltinType.AINT32);
-        }        
-        
+        }
+
         return new AUnionType(unionList, "String-length-Result");
-    }      
+    }
 }