diff --git a/src/process_pipeline.c b/src/process_pipeline.c
index dd5e4f4..830d2ad 100644
--- a/src/process_pipeline.c
+++ b/src/process_pipeline.c
@@ -401,7 +401,7 @@ process_image_for_capture(const uint8_t *image, int count)
 	// Write black thumbnail, only windows uses this
 	{
 		unsigned char *buf =
-			(unsigned char *)calloc(1, (int)mode.width >> 4);
+			(unsigned char *)calloc(1, (mode.width >> 4) * 3);
 		for (int row = 0; row < (mode.height >> 4); row++) {
 			TIFFWriteScanline(tif, buf, row, 0);
 		}