diff --git a/src/encoding/json/decode.go b/src/encoding/json/decode.go
index cbd71acfc6c38..df1c085917832 100644
--- a/src/encoding/json/decode.go
+++ b/src/encoding/json/decode.go
@@ -199,66 +199,6 @@ func (n Number) Int64() (int64, error) {
 	return strconv.ParseInt(string(n), 10, 64)
 }
 
-// isValidNumber reports whether s is a valid JSON number literal.
-func isValidNumber(s string) bool {
-	// This function implements the JSON numbers grammar.
-	// See https://tools.ietf.org/html/rfc7159#section-6
-	// and https://json.org/number.gif
-
-	if s == "" {
-		return false
-	}
-
-	// Optional -
-	if s[0] == '-' {
-		s = s[1:]
-		if s == "" {
-			return false
-		}
-	}
-
-	// Digits
-	switch {
-	default:
-		return false
-
-	case s[0] == '0':
-		s = s[1:]
-
-	case '1' <= s[0] && s[0] <= '9':
-		s = s[1:]
-		for len(s) > 0 && '0' <= s[0] && s[0] <= '9' {
-			s = s[1:]
-		}
-	}
-
-	// . followed by 1 or more digits.
-	if len(s) >= 2 && s[0] == '.' && '0' <= s[1] && s[1] <= '9' {
-		s = s[2:]
-		for len(s) > 0 && '0' <= s[0] && s[0] <= '9' {
-			s = s[1:]
-		}
-	}
-
-	// e or E followed by an optional - or + and
-	// 1 or more digits.
-	if len(s) >= 2 && (s[0] == 'e' || s[0] == 'E') {
-		s = s[1:]
-		if s[0] == '+' || s[0] == '-' {
-			s = s[1:]
-			if s == "" {
-				return false
-			}
-		}
-		for len(s) > 0 && '0' <= s[0] && s[0] <= '9' {
-			s = s[1:]
-		}
-	}
-
-	// Make sure we are at the end.
-	return s == ""
-}
-
 // decodeState represents the state while decoding a JSON value.
 type decodeState struct {
 	data         []byte
@@ -1027,10 +967,9 @@ func (d *decodeState) literalStore(item []byte, v reflect.Value, fromQuoted bool
 		switch v.Kind() {
 		default:
 			if v.Kind() == reflect.String && v.Type() == numberType {
+				// s must be a valid number, because it's
+				// already been tokenized.
 				v.SetString(s)
-				if !isValidNumber(s) {
-					return fmt.Errorf("json: invalid number literal, trying to unmarshal %q into Number", item)
-				}
 				break
 			}
 			if fromQuoted {
diff --git a/src/encoding/json/decode_test.go b/src/encoding/json/decode_test.go
index d66be44d4e134..8dcb08cbd2776 100644
--- a/src/encoding/json/decode_test.go
+++ b/src/encoding/json/decode_test.go
@@ -448,6 +448,7 @@ var unmarshalTests = []unmarshalTest{
 	{in: `[1, 2, 3+]`, err: &SyntaxError{"invalid character '+' after array element", 9}},
 	{in: `{"X":12x}`, err: &SyntaxError{"invalid character 'x' after object key:value pair", 8}, useNumber: true},
 	{in: `[2, 3`, err: &SyntaxError{msg: "unexpected end of JSON input", Offset: 5}},
+	{in: `{"F3": -}`, ptr: new(V), out: V{F3: Number("-")}, err: &SyntaxError{msg: "invalid character '}' in numeric literal", Offset: 9}},
 
 	// raw value errors
 	{in: "\x01 42", err: &SyntaxError{"invalid character '\\x01' looking for beginning of value", 1}},
diff --git a/src/encoding/json/encode.go b/src/encoding/json/encode.go
index 67412763d6400..07d3098f1c1ed 100644
--- a/src/encoding/json/encode.go
+++ b/src/encoding/json/encode.go
@@ -611,6 +611,66 @@ func stringEncoder(e *encodeState, v reflect.Value, opts encOpts) {
 	}
 }
 
+// isValidNumber reports whether s is a valid JSON number literal.
+func isValidNumber(s string) bool {
+	// This function implements the JSON numbers grammar.
+	// See https://tools.ietf.org/html/rfc7159#section-6
+	// and https://json.org/number.gif
+
+	if s == "" {
+		return false
+	}
+
+	// Optional -
+	if s[0] == '-' {
+		s = s[1:]
+		if s == "" {
+			return false
+		}
+	}
+
+	// Digits
+	switch {
+	default:
+		return false
+
+	case s[0] == '0':
+		s = s[1:]
+
+	case '1' <= s[0] && s[0] <= '9':
+		s = s[1:]
+		for len(s) > 0 && '0' <= s[0] && s[0] <= '9' {
+			s = s[1:]
+		}
+	}
+
+	// . followed by 1 or more digits.
+	if len(s) >= 2 && s[0] == '.' && '0' <= s[1] && s[1] <= '9' {
+		s = s[2:]
+		for len(s) > 0 && '0' <= s[0] && s[0] <= '9' {
+			s = s[1:]
+		}
+	}
+
+	// e or E followed by an optional - or + and
+	// 1 or more digits.
+	if len(s) >= 2 && (s[0] == 'e' || s[0] == 'E') {
+		s = s[1:]
+		if s[0] == '+' || s[0] == '-' {
+			s = s[1:]
+			if s == "" {
+				return false
+			}
+		}
+		for len(s) > 0 && '0' <= s[0] && s[0] <= '9' {
+			s = s[1:]
+		}
+	}
+
+	// Make sure we are at the end.
+	return s == ""
+}
+
 func interfaceEncoder(e *encodeState, v reflect.Value, opts encOpts) {
 	if v.IsNil() {
 		e.WriteString("null")