diff --git a/include/FLAC/encoder.h b/include/FLAC/encoder.h
index cad14a78..366ddde8 100644
--- a/include/FLAC/encoder.h
+++ b/include/FLAC/encoder.h
@@ -38,6 +38,7 @@ typedef enum {
 	FLAC__ENCODER_INVALID_QLP_COEFF_PRECISION,
 	FLAC__ENCODER_MID_SIDE_CHANNELS_MISMATCH,
 	FLAC__ENCODER_MID_SIDE_SAMPLE_SIZE_MISMATCH,
+	FLAC__ENCODER_ILLEGAL_MID_SIDE_FORCE,
 	FLAC__ENCODER_BLOCK_SIZE_TOO_SMALL_FOR_LPC_ORDER,
 	FLAC__ENCODER_NOT_STREAMABLE,
 	FLAC__ENCODER_FRAMING_ERROR,