diff --git a/encode_test.go b/encode_test.go
index 9c4ce9a..b2e5ec4 100644
--- a/encode_test.go
+++ b/encode_test.go
@@ -1893,3 +1893,22 @@ func TestIssue180(t *testing.T) {
 		t.Fatalf("failed to equal encoded result: expected %s but got %s", string(b1), string(b2))
 	}
 }
+
+func TestIssue235(t *testing.T) {
+	type TaskMessage struct {
+		Type      string
+		Payload   map[string]interface{}
+		UniqueKey string
+	}
+	msg := TaskMessage{
+		Payload: map[string]interface{}{
+			"sent_at": map[string]interface{}{
+				"Time":  "0001-01-01T00:00:00Z",
+				"Valid": false,
+			},
+		},
+	}
+	if _, err := json.Marshal(msg); err != nil {
+		t.Fatal(err)
+	}
+}
diff --git a/internal/encoder/opcode.go b/internal/encoder/opcode.go
index 220d5f3..15a695d 100644
--- a/internal/encoder/opcode.go
+++ b/internal/encoder/opcode.go
@@ -49,6 +49,23 @@ type Opcode struct {
 	DisplayKey string        // key text to display
 }
 
+func (c *Opcode) MaxIdx() uint32 {
+	max := uint32(0)
+	for _, value := range []uint32{
+		c.Idx,
+		c.ElemIdx,
+		c.Length,
+		c.MapIter,
+		c.MapPos,
+		c.Size,
+	} {
+		if max < value {
+			max = value
+		}
+	}
+	return max
+}
+
 func (c *Opcode) ToHeaderType(isString bool) OpType {
 	switch c.Op {
 	case OpInt:
@@ -338,7 +355,10 @@ func (c *Opcode) BeforeLastCode() *Opcode {
 func (c *Opcode) TotalLength() int {
 	var idx int
 	for code := c; code.Op != OpEnd; {
-		idx = int(code.Idx / uintptrSize)
+		maxIdx := int(code.MaxIdx() / uintptrSize)
+		if idx < maxIdx {
+			idx = maxIdx
+		}
 		if code.Op == OpRecursiveEnd {
 			break
 		}
@@ -349,7 +369,7 @@ func (c *Opcode) TotalLength() int {
 			code = code.Next
 		}
 	}
-	return idx + 2 // opEnd + 1
+	return idx + 1
 }
 
 func (c *Opcode) decOpcodeIndex() {