diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 5545eae..aa93377 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -7186,6 +7186,12 @@
 #define NEED_RETRY
 #endif
 
+/* INT_MAX is the theoretical largest chunk (or INT_MAX / 2 when
+   transcoding from UTF-16), but INT_MAX / 4 perfoms better in
+   both cases also and avoids partial characters overrunning the
+   length limit in MultiByteToWideChar on Windows */
+#define DECODING_CHUNK_SIZE (INT_MAX/4)
+
 #ifndef WC_ERR_INVALID_CHARS
 #  define WC_ERR_INVALID_CHARS 0x0080
 #endif
@@ -7422,8 +7428,8 @@
     do
     {
 #ifdef NEED_RETRY
-        if (size > INT_MAX) {
-            chunk_size = INT_MAX;
+        if (size > DECODING_CHUNK_SIZE) {
+            chunk_size = DECODING_CHUNK_SIZE;
             final = 0;
             done = 0;
         }
@@ -7827,10 +7833,8 @@
     do
     {
 #ifdef NEED_RETRY
-        /* UTF-16 encoding may double the size, so use only INT_MAX/2
-           chunks. */
-        if (len > INT_MAX/2) {
-            chunk_len = INT_MAX/2;
+        if (len > DECODING_CHUNK_SIZE) {
+            chunk_len = DECODING_CHUNK_SIZE;
             done = 0;
         }
         else