WhyNotHugo
diff --git a/Collapse file
‎barcode/isxn.py‎
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+1-1Lines changed: 1 addition & 1 deletion b/Collapse file
‎barcode/isxn.py‎
Copy file name to clipboardExpand all lines: barcode/isxn.py
+1-1Lines changed: 1 addition & 1 deletion
diff --git a/Collapse file
‎tests/test_checksums.py‎
Copy file name to clipboardExpand all lines: tests/test_checksums.py
+13Lines changed: 13 additions & 0 deletions b/Collapse file
‎tests/test_checksums.py‎
Copy file name to clipboardExpand all lines: tests/test_checksums.py
+13Lines changed: 13 additions & 0 deletions
@@ -113,7 +113,7 @@ def _calculate_checksum(self):
             11
             - sum(x * int(y) for x, y in enumerate(reversed(self.issn[:7]), start=2))
             % 11
-        )
+        ) % 11
         if tmp == 10:
             return "X"
 
 
@@ -46,3 +46,16 @@ def test_isbn13_checksum() -> None:
 def test_gs1_128_checksum() -> None:
     gs1_128 = get_barcode("gs1_128", "00376401856400470087")
     assert gs1_128.get_fullcode() == "00376401856400470087"
+
+
+def test_issn_checksum_zero() -> None:
+    # When the weighted sum is divisible by 11, the checksum should be 0,
+    # not 11. Regression test for issue #238.
+    issn = get_barcode("issn", "6727893")
+    assert issn.issn == "67278930"  # type: ignore[attr-defined]
+
+
+def test_issn_checksum_x() -> None:
+    # When (11 - weighted_sum % 11) % 11 == 10, checksum should be "X".
+    issn = get_barcode("issn", "0000006")
+    assert issn.issn == "0000006X"  # type: ignore[attr-defined]
Original file line number	Diff line number	Diff line change
`@@ -113,7 +113,7 @@ def _calculate_checksum(self):`
`113`	`113`	`11`
`114`	`114`	`- sum(x * int(y) for x, y in enumerate(reversed(self.issn[:7]), start=2))`
`115`	`115`	`% 11`
`116`		`- )`
	`116`	`+ ) % 11`
`117`	`117`	`if tmp == 10:`
`118`	`118`	`return "X"`
`119`	`119`