Reject stray carriage returns instead of truncating

svmloader.pyx

@@ -69,7 +69,10 @@ cdef _load_svmfile(fp, dtype, ltype, bint zero_based, bint multilabels):
 
         # process the line
         last_idx = -1
-        while s[0] != '#' and s[0] != '\n' and s[0] != '\r' and s[0] != 0:  # '\r': CRLF line ending
+        # A '\r' ends the line only when followed by '\n' (CRLF) or EOF.
+        # A stray '\r' is left to strtol(), which raises "invalid index".
+        while (s[0] != '#' and s[0] != '\n' and s[0] != 0
+               and not (s[0] == '\r' and (s[1] == '\n' or s[1] == 0))):
             # get index
             idx = strtol(s, &end, 10)
             if s == end:

tests/test_svmloader.py

@@ -166,6 +166,14 @@ def test_load_crlf_file(tmp_path):
     np.testing.assert_allclose(X.toarray(), [[0.5, 0.0, 2.0], [0.0, 1.0, 0.0]])
 
 
+def test_load_cr_only_file_is_rejected(tmp_path):
+    path = tmp_path / "cr_only.svm"
+    path.write_bytes(DATA.replace("\n", "\r").encode())
+
+    with pytest.raises(ValueError, match="invalid index"):
+        svmloader.load_svmfile(str(path), zero_based=False)
+
+
 def test_save_svmfile_writes_lf_line_endings(tmp_path):
     X = sp.csr_matrix(np.array([[0.0, 1.5], [2.0, 0.0]]))
     path = tmp_path / "out.svm"