diff --git a/src/encoding/json/decode.go b/src/encoding/json/decode.go
index 4319918d1e5..01af489b563 100644
--- a/src/encoding/json/decode.go
+++ b/src/encoding/json/decode.go
@@ -75,6 +75,8 @@ import (
 // either be any string type, an integer, implement json.Unmarshaler, or
 // implement encoding.TextUnmarshaler.
 //
+// If the JSON-encoded data contain a syntax error, Unmarshal returns a SyntaxError.
+//
 // If a JSON value is not appropriate for a given target type,
 // or if a JSON number overflows the target type, Unmarshal
 // skips that field and completes the unmarshaling as best it can.
diff --git a/src/encoding/json/scanner.go b/src/encoding/json/scanner.go
index dbaa821becc..22fc6922da9 100644
--- a/src/encoding/json/scanner.go
+++ b/src/encoding/json/scanner.go
@@ -27,6 +27,7 @@ func Valid(data []byte) bool {
 
 // checkValid verifies that data is valid JSON-encoded data.
 // scan is passed in for use by checkValid to avoid an allocation.
+// checkValid returns nil or a SyntaxError.
 func checkValid(data []byte, scan *scanner) error {
 	scan.reset()
 	for _, c := range data {
@@ -42,6 +43,7 @@ func checkValid(data []byte, scan *scanner) error {
 }
 
 // A SyntaxError is a description of a JSON syntax error.
+// Unmarshal will return a SyntaxError if the JSON can't be parsed.
 type SyntaxError struct {
 	msg    string // description of error
 	Offset int64  // error occurred after reading Offset bytes