diff --git a/src/PIL/Image.py b/src/PIL/Image.py
index 2e7abfb68c9..d0d48971369 100644
--- a/src/PIL/Image.py
+++ b/src/PIL/Image.py
@@ -1074,11 +1074,14 @@ def quantize(self, colors=256, method=None, kmeans=0, palette=None, dither=1):
 
         if method is None:
             # defaults:
-            method = 0
+            method = Image.MEDIANCUT
             if self.mode == "RGBA":
-                method = 2
+                method = Image.FASTOCTREE
 
-        if self.mode == "RGBA" and method not in (2, 3):
+        if self.mode == "RGBA" and method not in (
+            Image.FASTOCTREE,
+            Image.LIBIMAGEQUANT,
+        ):
             # Caller specified an invalid mode.
             raise ValueError(
                 "Fast Octree (method == 2) and libimagequant (method == 3) "