diff --git a/index_op_test.go b/index_op_test.go
index 5f752da..589c2e4 100644
--- a/index_op_test.go
+++ b/index_op_test.go
@@ -95,7 +95,7 @@ func TestArrayInStruct(t *testing.T) {
 }
 
 type StructWithMap struct {
-	Map map[string]string
+	Map map[string]int64
 }
 
 func TestMapField(t *testing.T) {
@@ -110,8 +110,8 @@ func TestMapField(t *testing.T) {
 	}
 
 	inputs := make(map[string]interface{})
-	mapField := make(map[string]string)
-	mapField["key"] = "value"
+	mapField := make(map[string]int64)
+	mapField["key"] = 42
 	inputs["s"] = &StructWithMap{
 		Map: mapField,
 	}
@@ -128,7 +128,46 @@ func TestMapField(t *testing.T) {
 		t.Fatal("Experiment run failed")
 	}
 
-	if elem := exp.Outputs["element"]; elem != "value" {
+	if elem := exp.Outputs["element"]; elem != int64(42) {
+		t.Fail()
+	}
+
+	if exp.Outputs["empty"] != nil {
+		t.Fail()
+	}
+}
+
+type StructWithNilField struct {
+	None interface{}
+}
+
+func TestStructWithNilField(t *testing.T) {
+	data, err := ioutil.ReadFile("test/struct_with_nil_field.json")
+	if err != nil {
+		t.Fatal(err)
+	}
+	var js map[string]interface{}
+	err = json.Unmarshal(data, &js)
+	if (err != nil) {
+		t.Fatal(err)
+	}
+
+	inputs := make(map[string]interface{})
+	inputs["struct"] = &StructWithNilField{}
+
+	exp := &Interpreter{
+		Name: "struct with nil field",
+		Salt: "safasdf",
+		Inputs: inputs,
+		Outputs: make(map[string]interface{}),
+		Code: js,
+	}
+
+	if _, ok := exp.Run(); !ok {
+		t.Fatal("Experiment run failed")
+	}
+
+	if exp.Outputs["nil"] != nil {
 		t.Fail()
 	}
 }
\ No newline at end of file
diff --git a/operators.go b/operators.go
index 1a57175..cf2865e 100644
--- a/operators.go
+++ b/operators.go
@@ -213,7 +213,11 @@ func unwrapValue(value reflect.Value) interface{} {
 	case reflect.Bool:
 		return value.Bool()
 	default:
-		return value.Interface()
+		if value.IsValid() {
+			return value.Interface()
+		} else {
+			return nil
+		}
 	}
 }
 
diff --git a/test/map_index_test.json b/test/map_index_test.json
index 7ce7cd1..9481e0c 100644
--- a/test/map_index_test.json
+++ b/test/map_index_test.json
@@ -32,6 +32,18 @@
         },
         "index": "key"
       }
+    },
+    {
+      "op": "set",
+      "var": "empty",
+      "value": {
+        "op": "index",
+        "base": {
+          "op": "get",
+          "var": "map"
+        },
+        "index": "not there"
+      }
     }
   ]
 }
\ No newline at end of file
diff --git a/test/struct_with_nil_field.json b/test/struct_with_nil_field.json
new file mode 100644
index 0000000..ad8e14b
--- /dev/null
+++ b/test/struct_with_nil_field.json
@@ -0,0 +1,12 @@
+{
+  "op": "set",
+  "var": "nil",
+  "value": {
+    "op": "index",
+    "base": {
+      "op": "get",
+      "var": "struct"
+    },
+    "index": "None"
+  }
+}
\ No newline at end of file