diff --git a/libavcodec/qtrle.c b/libavcodec/qtrle.c
index b66acd4..d68b44f 100644
--- a/libavcodec/qtrle.c
+++ b/libavcodec/qtrle.c
@@ -127,6 +127,7 @@
     while (lines_to_change--) {
         CHECK_STREAM_PTR(2);
         pixel_ptr = row_ptr + (num_pixels * (s->buf[stream_ptr++] - 1));
+        CHECK_PIXEL_PTR(0);  /* make sure pixel_ptr is positive */
 
         while ((rle_code = (signed char)s->buf[stream_ptr++]) != -1) {
             if (rle_code == 0) {
@@ -183,6 +184,7 @@
     while (lines_to_change--) {
         CHECK_STREAM_PTR(2);
         pixel_ptr = row_ptr + (4 * (s->buf[stream_ptr++] - 1));
+        CHECK_PIXEL_PTR(0);  /* make sure pixel_ptr is positive */
 
         while ((rle_code = (signed char)s->buf[stream_ptr++]) != -1) {
             if (rle_code == 0) {
@@ -236,6 +238,7 @@
     while (lines_to_change--) {
         CHECK_STREAM_PTR(2);
         pixel_ptr = row_ptr + (s->buf[stream_ptr++] - 1) * 2;
+        CHECK_PIXEL_PTR(0);  /* make sure pixel_ptr is positive */
 
         while ((rle_code = (signed char)s->buf[stream_ptr++]) != -1) {
             if (rle_code == 0) {
@@ -285,6 +288,7 @@
     while (lines_to_change--) {
         CHECK_STREAM_PTR(2);
         pixel_ptr = row_ptr + (s->buf[stream_ptr++] - 1) * 3;
+        CHECK_PIXEL_PTR(0);  /* make sure pixel_ptr is positive */
 
         while ((rle_code = (signed char)s->buf[stream_ptr++]) != -1) {
             if (rle_code == 0) {
@@ -336,6 +340,7 @@
     while (lines_to_change--) {
         CHECK_STREAM_PTR(2);
         pixel_ptr = row_ptr + (s->buf[stream_ptr++] - 1) * 4;
+        CHECK_PIXEL_PTR(0);  /* make sure pixel_ptr is positive */
 
         while ((rle_code = (signed char)s->buf[stream_ptr++]) != -1) {
             if (rle_code == 0) {