diff --git a/Tests/test_image_quantize.py b/Tests/test_image_quantize.py
index 8876285605a..ec1c13977d1 100644
--- a/Tests/test_image_quantize.py
+++ b/Tests/test_image_quantize.py
@@ -179,3 +179,14 @@ def test_small_palette() -> None:
     quantized_colors = im.getcolors()
     assert quantized_colors is not None
     assert len(quantized_colors) == 2
+
+
+def test_empty_palette() -> None:
+    im = hopper()
+
+    p = Image.new("P", (1, 1))
+    assert p.palette is not None
+    assert p.palette.palette == b""
+
+    with pytest.raises(ValueError, match="empty palette"):
+        im.quantize(palette=p)
diff --git a/src/libImaging/Convert.c b/src/libImaging/Convert.c
index b2b7ff26a22..5c3ec61c75b 100644
--- a/src/libImaging/Convert.c
+++ b/src/libImaging/Convert.c
@@ -1149,7 +1149,11 @@ topalette(
 
     alpha = mode == IMAGING_MODE_PA;
 
-    if (palette == NULL) {
+    if (palette != NULL) {
+        if (palette->size == 0) {
+            return (Imaging)ImagingError_ValueError("empty palette");
+        }
+    } else {
         /* FIXME: make user configurable */
         if (imIn->bands == 1) {
             palette = ImagingPaletteNew(IMAGING_MODE_RGB);
diff --git a/src/libImaging/Palette.c b/src/libImaging/Palette.c
index b2dacf656b5..ceb69d3dc6b 100644
--- a/src/libImaging/Palette.c
+++ b/src/libImaging/Palette.c
@@ -211,6 +211,7 @@ ImagingPaletteCacheUpdate(ImagingPalette palette, int r, int g, int b) {
 
     for (i = 0; i < BOXVOLUME; i++) {
         d[i] = (unsigned int)~0;
+        c[i] = 0;
     }
 
     for (i = 0; i < palette->size; i++) {