diff --git a/ext/mbstring/libmbfl/filters/mbfilter_cp5022x.c b/ext/mbstring/libmbfl/filters/mbfilter_cp5022x.c
index ff5cfb43086..f9e64c32589 100644
--- a/ext/mbstring/libmbfl/filters/mbfilter_cp5022x.c
+++ b/ext/mbstring/libmbfl/filters/mbfilter_cp5022x.c
@@ -847,11 +847,27 @@ static void mb_wchar_to_cp50220(uint32_t *in, size_t len, mb_convert_buf *buf, b
 	MB_CONVERT_BUF_ENSURE(buf, out, limit, len);
 
 	bool consumed = false;
+	uint32_t w;
+
+	if (buf->state & 0xFFFF00) {
+		/* Reprocess cached codepoint */
+		w = buf->state >> 8;
+		buf->state &= 0xFF;
+		goto reprocess_codepoint;
+	}
 
 	while (len--) {
-		uint32_t w = *in++;
+		w = *in++;
+reprocess_codepoint:
 
-		w = mbfl_convert_kana(w, len ? *in : 0, &consumed, NULL, MBFL_HAN2ZEN_KATAKANA | MBFL_HAN2ZEN_GLUE);
+		if (w >= 0xFF61 && w <= 0xFF9F && !len && !end) {
+			/* This codepoint may need to combine with the next one,
+			 * but the 'next one' will come in a separate buffer */
+			buf->state |= w << 8;
+			break;
+		} else {
+			w = mbfl_convert_kana(w, len ? *in : 0, &consumed, NULL, MBFL_HAN2ZEN_KATAKANA | MBFL_HAN2ZEN_GLUE);
+		}
 
 		if (consumed) {
 			/* Two successive codepoints were converted into one */
diff --git a/ext/mbstring/tests/cp5022x_encoding.phpt b/ext/mbstring/tests/cp5022x_encoding.phpt
index 04a9c015536..f8e5831ebe2 100644
--- a/ext/mbstring/tests/cp5022x_encoding.phpt
+++ b/ext/mbstring/tests/cp5022x_encoding.phpt
@@ -382,6 +382,14 @@ $converted = mb_convert_encoding("\xff\xff\x00&", 'CP50220', 'UTF-16BE');
 if ($converted !== '?&')
   die("Bad handling of erroneous codepoint followed by good one (got " . bin2hex($converted) . ")");
 
+// In CP50220, two codepoints can be collapsed into a single kuten code in some cases
+// This should work even on a boundary between separately processed buffers
+$shouldCollapse = "\xFF\x76\xFF\x9E";
+$expected = "\x1B\$B%,\x1B(B";
+for ($i = 0; $i < 256; $i++) {
+  convertValidString(str_repeat("\x00a", $i) . $shouldCollapse, str_repeat('a', $i) . $expected, 'UTF-16BE', 'CP50220', false);
+}
+
 ?>
 --EXPECT--
 ASCII support OK