diff --git a/libavcodec/flashsv2enc.c b/libavcodec/flashsv2enc.c
index 5139b17a2856c2725a12f0f050870d7f1ac70d6e..430b6806c8828bc2e891592b94d73c867322e500 100644
--- a/libavcodec/flashsv2enc.c
+++ b/libavcodec/flashsv2enc.c
@@ -142,6 +142,7 @@ static void init_blocks(FlashSV2Context * s, Block * blocks,
 {
     int row, col;
     Block *b;
+    memset(blocks, 0, s->cols * s->rows * sizeof(*blocks));
     for (col = 0; col < s->cols; col++) {
         for (row = 0; row < s->rows; row++) {
             b = blocks + (col + row * s->cols);