3 files changed, 41 insertions, 1 deletions
diff --git a/src/encoding/json/stream_test.go b/src/encoding/json/stream_test.go
index 0e937cfaa1..ba3bc4002b 100644
--- a/src/encoding/json/stream_test.go
+++ b/src/encoding/json/stream_test.go
@@ -459,6 +459,9 @@ func TestDecodeInStream(t *testing.T) {
 		{CaseName: Name(""), json: ` \a`, expTokens: []any{
 			&SyntaxError{"invalid character '\\\\' looking for beginning of value", 1},
 		}},
+		{CaseName: Name(""), json: `,`, expTokens: []any{
+			&SyntaxError{"invalid character ',' looking for beginning of value", 0},
+		}},
 	}
 	for _, tt := range tests {
 		t.Run(tt.Name, func(t *testing.T) {
@@ -467,6 +470,15 @@ func TestDecodeInStream(t *testing.T) {
 				var got any
 				var err error
 
+				wantMore := true
+				switch want {
+				case Delim(']'), Delim('}'):
+					wantMore = false
+				}
+				if got := dec.More(); got != wantMore {
+					t.Fatalf("%s:\n\tinput: %s\n\tdec.More() = %v, want %v (next token: %T(%v))", tt.Where, tt.json, got, wantMore, want, want)
+				}
+
 				if dt, ok := want.(decodeThis); ok {
 					want = dt.v
 					err = dec.Decode(&got)
diff --git a/src/encoding/json/v2_stream.go b/src/encoding/json/v2_stream.go
index dcee553ee1..ca0822cb73 100644
--- a/src/encoding/json/v2_stream.go
+++ b/src/encoding/json/v2_stream.go
@@ -197,6 +197,9 @@ func (d Delim) String() string {
 // to mark the start and end of arrays and objects.
 // Commas and colons are elided.
 func (dec *Decoder) Token() (Token, error) {
+	if dec.err != nil {
+		return nil, dec.err
+	}
 	tok, err := dec.dec.ReadToken()
 	if err != nil {
 		// Historically, v1 would report just [io.EOF] if
@@ -238,7 +241,20 @@ func (dec *Decoder) Token() (Token, error) {
 func (dec *Decoder) More() bool {
 	dec.hadPeeked = true
 	k := dec.dec.PeekKind()
-	return k > 0 && k != ']' && k != '}'
+	if k == 0 {
+		if dec.err == nil {
+			// PeekKind doesn't distinguish between EOF and error,
+			// so read the next token to see which we get.
+			_, err := dec.dec.ReadToken()
+			if err == nil {
+				// This is only possible if jsontext violates its documentation.
+				err = errors.New("json: successful read after failed peek")
+			}
+			dec.err = transformSyntacticError(err)
+		}
+		return dec.err != io.EOF
+	}
+	return k != ']' && k != '}'
 }
 
 // InputOffset returns the input stream byte offset of the current decoder position.
diff --git a/src/encoding/json/v2_stream_test.go b/src/encoding/json/v2_stream_test.go
index 0885631fb5..d7f9f11084 100644
--- a/src/encoding/json/v2_stream_test.go
+++ b/src/encoding/json/v2_stream_test.go
@@ -439,6 +439,9 @@ func TestDecodeInStream(t *testing.T) {
 		{CaseName: Name(""), json: ` \a`, expTokens: []any{
 			&SyntaxError{"invalid character '\\\\' looking for beginning of value", len64(` `)},
 		}},
+		{CaseName: Name(""), json: `,`, expTokens: []any{
+			&SyntaxError{"invalid character ',' looking for beginning of value", 0},
+		}},
 	}
 	for _, tt := range tests {
 		t.Run(tt.Name, func(t *testing.T) {
@@ -447,6 +450,15 @@ func TestDecodeInStream(t *testing.T) {
 				var got any
 				var err error
 
+				wantMore := true
+				switch want {
+				case Delim(']'), Delim('}'):
+					wantMore = false
+				}
+				if got := dec.More(); got != wantMore {
+					t.Fatalf("%s:\n\tinput: %s\n\tdec.More() = %v, want %v (next token: %T(%v)) rem:%q", tt.Where, tt.json, got, wantMore, want, want, tt.json[dec.InputOffset():])
+				}
+
 				if dt, ok := want.(decodeThis); ok {
 					want = dt.v
 					err = dec.Decode(&got)