diff --git a/NEWS b/NEWS
index ae3c521c60b55..482ccc4a5604d 100644
--- a/NEWS
+++ b/NEWS
@@ -21,6 +21,8 @@ PHP                                                                        NEWS
   . mb_detect_encoding recognizes all letters in Czech alphabet (alexdowad)
   . mb_detect_encoding recognizes all letters in Hungarian alphabet (alexdowad)
   . Fixed bug GH-8685 (pcre not ready at mbstring startup). (Remi)
+  . Fixed bug GH-8281 (mb_convert_encoding "\" and "~" convert failed to
+    Shift_JIS). (alexdowad)
 
 - OPcache:
   . Fixed bug GH-8591 (tracing JIT crash after private instance method change).
diff --git a/ext/mbstring/libmbfl/filters/mbfilter_sjis.c b/ext/mbstring/libmbfl/filters/mbfilter_sjis.c
index 188f162bf8785..96456b26e7eb6 100644
--- a/ext/mbstring/libmbfl/filters/mbfilter_sjis.c
+++ b/ext/mbstring/libmbfl/filters/mbfilter_sjis.c
@@ -141,11 +141,7 @@ int mbfl_filt_conv_sjis_wchar(int c, mbfl_convert_filter *filter)
 
 	switch (filter->status) {
 	case 0:
-		if (c == 0x5C) {
-			CK((*filter->output_function)(0xA5, filter->data));
-		} else if (c == 0x7E) {
-			CK((*filter->output_function)(0x203E, filter->data));
-		} else if (c >= 0 && c < 0x80) { /* ASCII */
+		if (c >= 0 && c < 0x80) { /* ASCII */
 			CK((*filter->output_function)(c, filter->data));
 		} else if (c > 0xA0 && c < 0xE0) { /* Kana */
 			CK((*filter->output_function)(0xFEC0 + c, filter->data));
@@ -197,17 +193,7 @@ int mbfl_filt_conv_wchar_sjis(int c, mbfl_convert_filter *filter)
 	int c1, c2, s1, s2;
 
 	s1 = 0;
-	if (c == 0x5C) {
-		/* Unicode 0x5C is a backslash; but Shift-JIS uses 0x5C for the
-		 * Yen sign. JIS X 0208 kuten 0x2140 is a backslash. */
-		s1 = 0x2140;
-	} else if (c == 0x7E) {
-		/* Unicode 0x7E is a tilde, but Shift-JIS uses 0x7E for overline (or
-		 * macron). JIS X 0208 kuten 0x2141 is 'WAVE DASH' */
-		s1 = 0x2141;
-	} else if (c == 0xAF || c == 0x203E) { /* U+00AF is MACRON, U+203E is OVERLINE */
-		s1 = 0x7E; /* Halfwidth overline/macron */
-	} else if (c >= ucs_a1_jis_table_min && c < ucs_a1_jis_table_max) {
+	if (c >= ucs_a1_jis_table_min && c < ucs_a1_jis_table_max) {
 		s1 = ucs_a1_jis_table[c - ucs_a1_jis_table_min];
 	} else if (c >= ucs_a2_jis_table_min && c < ucs_a2_jis_table_max) {
 		s1 = ucs_a2_jis_table[c - ucs_a2_jis_table_min];
@@ -218,7 +204,9 @@ int mbfl_filt_conv_wchar_sjis(int c, mbfl_convert_filter *filter)
 	}
 	if (s1 <= 0) {
 		if (c == 0xA5) { /* YEN SIGN */
-			s1 = 0x5C;
+			s1 = 0x216F; /* FULLWIDTH YEN SIGN */
+		} else if (c == 0xAF || c == 0x203E) { /* U+00AF is MACRON, U+203E is OVERLINE */
+			s1 = 0x2131; /* FULLWIDTH MACRON */
 		} else if (c == 0xFF3C) { /* FULLWIDTH REVERSE SOLIDUS */
 			s1 = 0x2140;
 		} else if (c == 0xFF5E) { /* FULLWIDTH TILDE */
diff --git a/ext/mbstring/tests/sjis_encoding.phpt b/ext/mbstring/tests/sjis_encoding.phpt
index aece04b0f2221..c94cc464714c1 100644
--- a/ext/mbstring/tests/sjis_encoding.phpt
+++ b/ext/mbstring/tests/sjis_encoding.phpt
@@ -20,13 +20,37 @@ for ($i = 0; $i < 0x20; $i++) {
   $fromUnicode["\x00" . chr($i)] = chr($i);
 }
 
-/* U+007E is TILDE; convert to Shift-JIS 0x8160 (WAVE DASH) */
-$fromUnicode["\x00\x7E"] = "\x81\x60";
+/* According to the relevant Japan Industrial Standards Committee standards,
+ * SJIS 0x5C is a Yen sign, and 0x7E is an overline.
+ *
+ * However, this conflicts with the implementation of SJIS in various legacy
+ * software (notably Microsoft products), where SJIS 0x5C and 0x7E are taken
+ * as equivalent to the same ASCII bytes.
+ *
+ * Prior to PHP 8.1, mbstring's implementation of SJIS handled these bytes
+ * compatibly with Microsoft products. This was changed in PHP 8.1.0, in an
+ * attempt to comply with the JISC specifications. However, after discussion
+ * with various concerned Japanese developers, it seems that the historical
+ * behavior was more useful in the majority of applications which process
+ * SJIS-encoded text. */
+$validChars["\x5C"] = "\x00\x5C";
+$validChars["\x7E"] = "\x00\x7E";
+$fromUnicode["\x00\x5C"] = "\x5C";
+$fromUnicode["\x00\x7E"] = "\x7E";
+
+/* That means it does not make sense to convert U+203E (OVERLINE)
+ * to 0x7E; convert it to JIS X 0208 FULLWIDTH MACRON instead */
+$fromUnicode["\x20\x3E"] = "\x81\x50";
+/* U+00AF is MACRON; convert that to FULLWIDTH MACRON as well */
+$fromUnicode["\x00\xAF"] = "\x81\x50";
+/* Since we are treating 0x5C as equivalent to U+005C, it does not
+ * make sense to convert U+00A5 (YEN SIGN) to 0x5C
+ * Convert it to JIS X 0208 FULLWIDTH YEN SIGN instead */
+$fromUnicode["\x00\xA5"] = "\x81\x8F";
+
 /* DEL character */
 $validChars["\x7F"] = "\x00\x7F";
 $fromUnicode["\x00\x7F"] = "\x7F";
-/* U+00AF is MACRON; Shift-JIS 0x7E is overline */
-$fromUnicode["\x00\xAF"] = "\x7E";
 /* Use fullwidth reverse solidus, not (halfwidth) backslash (0x5C) */
 $validChars["\x81\x5F"] = "\xFF\x3C";
 $fromUnicode["\xFF\x3C"] = "\x81\x5F";