diff --git a/v1/tasks/reflect.go b/v1/tasks/reflect.go
index 53aa7eb7..a17a04b5 100644
--- a/v1/tasks/reflect.go
+++ b/v1/tasks/reflect.go
@@ -6,6 +6,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"reflect"
+	"strconv"
 	"strings"
 )
 
@@ -288,21 +289,21 @@ func getIntValue(theType string, value interface{}) (int64, error) {
 }
 
 func getUintValue(theType string, value interface{}) (uint64, error) {
-	// We use https://golang.org/pkg/encoding/json/#Decoder.UseNumber when unmarshaling signatures.
-	// This is because JSON only supports 64-bit floating point numbers and we could lose precision
-	// when converting from float64 to unsigned integer
+	// Losing precision only happens in receiving a JSON number from a language like js,
+	// and receiving a large uint number from golang or python could cause json.Number.Int64 be turned into a panic.
+	// So we use strconv.ParseUint to correctly parse a uint value.
 	if strings.HasPrefix(fmt.Sprintf("%T", value), "json.Number") {
 		n, ok := value.(json.Number)
 		if !ok {
 			return 0, typeConversionError(value, typesMap[theType].String())
 		}
 
-		intVal, err := n.Int64()
+		uintVal, err := strconv.ParseUint(string(n), 10, 64)
 		if err != nil {
 			return 0, err
 		}
 
-		return uint64(intVal), nil
+		return uintVal, nil
 	}
 
 	var n uint64
diff --git a/v1/tasks/reflect_test.go b/v1/tasks/reflect_test.go
index 8593666c..392af5e4 100644
--- a/v1/tasks/reflect_test.go
+++ b/v1/tasks/reflect_test.go
@@ -81,6 +81,12 @@ var (
 			expectedType:  "uint64",
 			expectedValue: uint64(185135722552891243),
 		},
+		{
+			name:          "uint64",
+			value:         json.Number("9223372036854775808"), // math.MaxInt64 + 1
+			expectedType:  "uint64",
+			expectedValue: uint64(9223372036854775808),
+		},
 		{
 			name:          "float32",
 			value:         json.Number("0.5"),
diff --git a/v2/tasks/reflect.go b/v2/tasks/reflect.go
index 53aa7eb7..a17a04b5 100644
--- a/v2/tasks/reflect.go
+++ b/v2/tasks/reflect.go
@@ -6,6 +6,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"reflect"
+	"strconv"
 	"strings"
 )
 
@@ -288,21 +289,21 @@ func getIntValue(theType string, value interface{}) (int64, error) {
 }
 
 func getUintValue(theType string, value interface{}) (uint64, error) {
-	// We use https://golang.org/pkg/encoding/json/#Decoder.UseNumber when unmarshaling signatures.
-	// This is because JSON only supports 64-bit floating point numbers and we could lose precision
-	// when converting from float64 to unsigned integer
+	// Losing precision only happens in receiving a JSON number from a language like js,
+	// and receiving a large uint number from golang or python could cause json.Number.Int64 be turned into a panic.
+	// So we use strconv.ParseUint to correctly parse a uint value.
 	if strings.HasPrefix(fmt.Sprintf("%T", value), "json.Number") {
 		n, ok := value.(json.Number)
 		if !ok {
 			return 0, typeConversionError(value, typesMap[theType].String())
 		}
 
-		intVal, err := n.Int64()
+		uintVal, err := strconv.ParseUint(string(n), 10, 64)
 		if err != nil {
 			return 0, err
 		}
 
-		return uint64(intVal), nil
+		return uintVal, nil
 	}
 
 	var n uint64
diff --git a/v2/tasks/reflect_test.go b/v2/tasks/reflect_test.go
index 3fe9e692..1892ca31 100644
--- a/v2/tasks/reflect_test.go
+++ b/v2/tasks/reflect_test.go
@@ -81,6 +81,12 @@ var (
 			expectedType:  "uint64",
 			expectedValue: uint64(185135722552891243),
 		},
+		{
+			name:          "uint64",
+			value:         json.Number("9223372036854775808"), // math.MaxInt64 + 1
+			expectedType:  "uint64",
+			expectedValue: uint64(9223372036854775808),
+		},
 		{
 			name:          "float32",
 			value:         json.Number("0.5"),