diff --git a/libImaging/BcnDecode.c b/libImaging/BcnDecode.c
index b24a3ebb5..58d3ecc10 100644
--- a/libImaging/BcnDecode.c
+++ b/libImaging/BcnDecode.c
@@ -815,6 +815,7 @@ static int decode_bcn(Imaging im, ImagingCodecState state, const UINT8* src, int
 	case NN: \
 		while (bytes >= SZ) { \
 			TY col[16]; \
+			memset(col, 0, 16 * sizeof(col[0])); \
 			decode_bc##NN##_block(col, ptr); \
 			put_block(im, state, (const char *)col, sizeof(col[0]), C); \
 			ptr += SZ; \