diff --git a/lib/go/thrift/simple_json_protocol.go b/lib/go/thrift/simple_json_protocol.go
index ec12991a1d..6ae3cba566 100644
--- a/lib/go/thrift/simple_json_protocol.go
+++ b/lib/go/thrift/simple_json_protocol.go
@@ -432,7 +432,13 @@ func (p *TSimpleJSONProtocol) ReadMapBegin(ctx context.Context) (keyType TType,
 	if err != nil {
 		return keyType, valueType, 0, err
 	}
-	err = checkSizeForProtocol(int32(size), p.cfg)
+	if iSize > math.MaxInt32 {
+		return keyType, valueType, 0, NewTProtocolExceptionWithType(
+			SIZE_LIMIT,
+			fmt.Errorf("size exceeded max allowed: %d", iSize),
+		)
+	}
+	err = checkSizeForProtocol(int32(iSize), p.cfg)
 	if err != nil {
 		return keyType, valueType, 0, err
 	}
diff --git a/lib/go/thrift/simple_json_protocol_test.go b/lib/go/thrift/simple_json_protocol_test.go
index 18650989a0..e7f2ac95a7 100644
--- a/lib/go/thrift/simple_json_protocol_test.go
+++ b/lib/go/thrift/simple_json_protocol_test.go
@@ -791,3 +791,44 @@ func TestJSONContextStack(t *testing.T) {
 func TestTSimpleJSONProtocolUnmatchedBeginEnd(t *testing.T) {
 	UnmatchedBeginEndProtocolTest(t, NewTSimpleJSONProtocolFactory())
 }
+
+func TestReadSimpleJSONProtocolMapBeginSizeLimit(t *testing.T) {
+	ctx := context.Background()
+	trans := NewTMemoryBuffer()
+	wp := NewTSimpleJSONProtocol(trans)
+	if err := wp.WriteMapBegin(ctx, STRING, STRING, 1<<30); err != nil {
+		t.Fatal(err)
+	}
+	if err := wp.Flush(ctx); err != nil {
+		t.Fatal(err)
+	}
+
+	rp := NewTSimpleJSONProtocolConf(trans, &TConfiguration{MaxMessageSize: 1024})
+	_, _, size, err := rp.ReadMapBegin(ctx)
+	if err == nil {
+		t.Fatalf("expected size-limit error reading oversized map, got nil with size %d", size)
+	}
+	if terr, ok := err.(TProtocolException); !ok || terr.TypeId() != SIZE_LIMIT {
+		t.Errorf("expected SIZE_LIMIT protocol exception, got %v", err)
+	}
+}
+
+func TestReadSimpleJSONProtocolMapBeginSizeOverflow(t *testing.T) {
+	// iSize = 1<<32 + 1; int32 narrowing wraps it to 1, which would pass checkSizeForProtocol.
+	// The map header is written directly as raw JSON to avoid int-width issues on 32-bit platforms.
+	overflowSize := int64(math.MaxInt32)*2 + 3 // = 4294967297 = 1<<32 + 1
+	buf := NewTMemoryBuffer()
+	buf.WriteString(fmt.Sprintf("[%d,%d,%d]", I32, I32, overflowSize))
+	proto := NewTSimpleJSONProtocolConf(buf, &TConfiguration{MaxMessageSize: 1024})
+	_, _, _, err := proto.ReadMapBegin(context.Background())
+	if err == nil {
+		t.Fatal("expected error, got nil")
+	}
+	tpe, ok := err.(TProtocolException)
+	if !ok {
+		t.Fatalf("expected TProtocolException, got %T: %v", err, err)
+	}
+	if tpe.TypeId() != SIZE_LIMIT {
+		t.Errorf("expected SIZE_LIMIT, got %d: %v", tpe.TypeId(), err)
+	}
+}