diff --git a/main/src/com/google/refine/expr/functions/Jsonize.java b/main/src/com/google/refine/expr/functions/Jsonize.java
index 10ea0c3ad..464d3436a 100644
--- a/main/src/com/google/refine/expr/functions/Jsonize.java
+++ b/main/src/com/google/refine/expr/functions/Jsonize.java
@@ -36,7 +36,10 @@ package com.google.refine.expr.functions;
 import java.io.IOException;
 import java.util.Properties;
 
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.google.refine.expr.EvalError;
 import com.google.refine.grel.Function;
+import com.google.refine.grel.ControlFunctionRegistry;
 import com.google.refine.util.ParsingUtilities;
 
 public class Jsonize implements Function {
@@ -45,12 +48,13 @@ public class Jsonize implements Function {
     public Object call(Properties bindings, Object[] args) {
         if (args.length >= 1) {
             try {
-                return ParsingUtilities.mapper.writeValueAsString(args[0]);
+                return ParsingUtilities.mapper.writerWithDefaultPrettyPrinter().writeValueAsString(args[0]);
             } catch (IOException e) {
                 throw new RuntimeException(e);
             }
         }
-        return null;
+        String errorMessage = " accepts a single argument";
+        return new EvalError(ControlFunctionRegistry.getFunctionName(this) + errorMessage);
     }
 
     
diff --git a/main/tests/server/src/com/google/refine/expr/functions/JsonizeTests.java b/main/tests/server/src/com/google/refine/expr/functions/JsonizeTests.java
index aa51f3c78..9e7ba61ac 100644
--- a/main/tests/server/src/com/google/refine/expr/functions/JsonizeTests.java
+++ b/main/tests/server/src/com/google/refine/expr/functions/JsonizeTests.java
@@ -26,10 +26,33 @@
  ******************************************************************************/
 package com.google.refine.expr.functions;
 
+import static org.testng.Assert.assertEquals;
+import static org.testng.Assert.assertTrue;
+
 import org.testng.annotations.Test;
 
+import com.google.refine.RefineTest;
+import com.google.refine.expr.EvalError;
+import com.google.refine.expr.util.CalendarParser;
+import com.google.refine.expr.util.CalendarParserException;
 import com.google.refine.util.TestUtils;
 
-public class JsonizeTests {
+public class JsonizeTests extends RefineTest {
+
+    @Test
+    public void testToString() throws CalendarParserException {
+
+        assertTrue(invoke("jsonize") instanceof EvalError);
+
+        Object[] emptyArray = {};
+        assertEquals(invoke("jsonize", (Object) emptyArray), "[ ]");
+
+        Object[] objArray = {4, "hello", true, 0.01, null};
+        assertEquals(invoke("jsonize", (Object) objArray), "[ 4, \"hello\", true, 0.01, null ]");
+
+        Object[][] multiArray = {{"OpenRefine", 12}, {13, 4.6}, {"data", "mining"}};
+        assertEquals(invoke("jsonize", (Object) multiArray), "[ [ \"OpenRefine\", 12 ], [ 13, 4.6 ], [ \"data\", \"mining\" ] ]");
+
+    }
 }
 
diff --git a/main/tests/server/src/com/google/refine/grel/FunctionTests.java b/main/tests/server/src/com/google/refine/grel/FunctionTests.java
index 1bf04b96e..481cc5429 100644
--- a/main/tests/server/src/com/google/refine/grel/FunctionTests.java
+++ b/main/tests/server/src/com/google/refine/grel/FunctionTests.java
@@ -109,7 +109,7 @@ public class FunctionTests extends RefineTest {
         Set<String> valid0args = new HashSet<>(Arrays.asList("now")); // valid 0-arg returns datetype
         // Not sure which, if any, of these are intended, but fixing them may break existing scripts
         Set<String> returnsNull = new HashSet<>(Arrays.asList("chomp", "contains", "escape", "unescape", "exp",
-                "fingerprint", "get", "jsonize", "parseJson", "partition", "pow", "rpartition",
+                "fingerprint", "get", "parseJson", "partition", "pow", "rpartition",
                 "slice", "substring", // synonyms for Slice
                 "unicode", "unicodeType"
                 ));