diff --git a/libswscale/output.c b/libswscale/output.c
index aa6e70db66..0ff0bf464f 100644
--- a/libswscale/output.c
+++ b/libswscale/output.c
@@ -643,7 +643,7 @@ yuv2mono_2_c_template(SwsContext *c, const int16_t *buf[2],
 
     if (c->dither == SWS_DITHER_ED) {
         int err = 0;
-        int acc = 0;
+        unsigned acc = 0;
         for (i = 0; i < dstW; i +=2) {
             int Y;
 
@@ -665,7 +665,8 @@ yuv2mono_2_c_template(SwsContext *c, const int16_t *buf[2],
         c->dither_error[0][i] = err;
     } else {
         for (i = 0; i < dstW; i += 8) {
-            int Y, acc = 0;
+            int Y;
+            unsigned acc = 0;
 
             Y = (buf0[i + 0] * yalpha1 + buf1[i + 0] * yalpha) >> 19;
             accumulate_bit(acc, Y + d128[0]);
@@ -700,7 +701,7 @@ yuv2mono_1_c_template(SwsContext *c, const int16_t *buf0,
 
     if (c->dither == SWS_DITHER_ED) {
         int err = 0;
-        int acc = 0;
+        unsigned acc = 0;
         for (i = 0; i < dstW; i +=2) {
             int Y;
 
@@ -722,7 +723,7 @@ yuv2mono_1_c_template(SwsContext *c, const int16_t *buf0,
         c->dither_error[0][i] = err;
     } else {
         for (i = 0; i < dstW; i += 8) {
-            int acc = 0;
+            unsigned acc = 0;
             accumulate_bit(acc, ((buf0[i + 0] + 64) >> 7) + d128[0]);
             accumulate_bit(acc, ((buf0[i + 1] + 64) >> 7) + d128[1]);
             accumulate_bit(acc, ((buf0[i + 2] + 64) >> 7) + d128[2]);