diff --git a/Tests/test_file_gif.py b/Tests/test_file_gif.py
index 90943ac8f69..198e1b16277 100644
--- a/Tests/test_file_gif.py
+++ b/Tests/test_file_gif.py
@@ -74,10 +74,10 @@ def test_bilevel(optimize):
         im.save(test_file, "GIF", optimize=optimize)
         return len(test_file.getvalue())
 
-    assert test_grayscale(0) == 800
-    assert test_grayscale(1) == 44
-    assert test_bilevel(0) == 800
-    assert test_bilevel(1) == 800
+    assert test_grayscale(0) == 799
+    assert test_grayscale(1) == 43
+    assert test_bilevel(0) == 799
+    assert test_bilevel(1) == 799
 
 
 def test_optimize_correctness():
diff --git a/src/libImaging/GifEncode.c b/src/libImaging/GifEncode.c
index e9c6c314918..a0fef993320 100644
--- a/src/libImaging/GifEncode.c
+++ b/src/libImaging/GifEncode.c
@@ -233,8 +233,13 @@ ImagingGifEncode(Imaging im, ImagingCodecState state, UINT8* buf, int bytes)
                         }
 
                 }
-
-                this = state->buffer[state->x++];
+                /* Potential special case for xsize==1 */
+                if (state->x < state->xsize) {
+                    this = state->buffer[state->x++];
+                } else {
+                    EMIT_RUN(label0);
+                    break;
+                }
 
                 if (this == context->last) {
                     context->count++;