diff --git a/libavcodec/proresdec2.c b/libavcodec/proresdec2.c
index 374c5cb8ad..5037bb8e02 100644
--- a/libavcodec/proresdec2.c
+++ b/libavcodec/proresdec2.c
@@ -458,7 +458,7 @@ static void unpack_alpha(GetBitContext *gb, uint16_t *dst, int num_coeffs,
             } else {
                 dst[idx++] = (alpha_val << 2) | (alpha_val >> 6);
             }
-            if (idx == num_coeffs - 1)
+            if (idx >= num_coeffs)
                 break;
         } while (get_bits_left(gb)>0 && get_bits1(gb));
         val = get_bits(gb, 4);
diff --git a/libavcodec/proresdec_lgpl.c b/libavcodec/proresdec_lgpl.c
index 73a1f6c0d0..5e98d55417 100644
--- a/libavcodec/proresdec_lgpl.c
+++ b/libavcodec/proresdec_lgpl.c
@@ -496,7 +496,7 @@ static void unpack_alpha(GetBitContext *gb, uint16_t *dst, int num_coeffs,
                 dst[idx++] = alpha_val >> 6;
             else
                 dst[idx++] = (alpha_val << 2) | (alpha_val >> 6);
-            if (idx == num_coeffs - 1)
+            if (idx >= num_coeffs)
                 break;
         } while (get_bits1(gb));
         val = get_bits(gb, 4);
diff --git a/tests/ref/fate/prores-transparency b/tests/ref/fate/prores-transparency
index 3842970cd2..9c71d33e76 100644
--- a/tests/ref/fate/prores-transparency
+++ b/tests/ref/fate/prores-transparency
@@ -1,5 +1,5 @@
 #tb 0: 1/25
 #tb 1: 1/48000
-0,          0,          0,        1, 16588800, 0x87f98f3c
+0,          0,          0,        1, 16588800, 0x20778f5e
 1,          0,          0,     1024,     4096, 0x00000000
 1,       1024,       1024,      896,     3584, 0x00000000