diff --git a/src/uucore/src/lib/features/checksum/validate.rs b/src/uucore/src/lib/features/checksum/validate.rs
index bb47ff6c920..f755d5283d1 100644
--- a/src/uucore/src/lib/features/checksum/validate.rs
+++ b/src/uucore/src/lib/features/checksum/validate.rs
@@ -281,6 +281,9 @@ impl LineFormat {
         // tagged format does not put a space before (filename)
 
         let par_idx = rest.iter().position(|&b| b == b'(')?;
+        if par_idx < 1 {
+            return None;
+        }
         let sub_case = if rest[par_idx - 1] == b' ' {
             SubCase::Posix
         } else {
@@ -1024,6 +1027,7 @@ mod tests {
     #[test]
     fn test_algo_based_parser() {
         #[allow(clippy::type_complexity)]
+        // Tuple format: (input line, option(algo name, option(algo bit size), filename, checksum)
         let test_cases: &[(&[u8], Option<(&[u8], Option<&[u8]>, &[u8], &[u8])>)] = &[
             (b"SHA256 (example.txt) = d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2", Some((b"SHA256", None, b"example.txt", b"d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2d2"))),
             // cspell:disable
@@ -1041,6 +1045,10 @@ mod tests {
             (b" MD5(weirdfilename6) = ) = fds65dsf46as5df4d6f54asds5d7f7g9", None),
             (b" MD5 (weirdfilename7)= )= fds65dsf46as5df4d6f54asds5d7f7g9", None),
             (b" MD5 (weirdfilename8) = )= fds65dsf46as5df4d6f54asds5d7f7g9", None),
+            // test for missing algorithm
+            (b"(filename) = fds65dsf46as5df4d6f54asds5d7f7g9", None),
+            (b"filename) = fds65dsf46as5df4d6f54asds5d7f7g9", None),
+            (b"filename = fds65dsf46as5df4d6f54asds5d7f7g9", None),
         ];
 
         // cspell:enable
diff --git a/tests/by-util/test_cksum.rs b/tests/by-util/test_cksum.rs
index 16ed6d8b373..b80d0a99456 100644
--- a/tests/by-util/test_cksum.rs
+++ b/tests/by-util/test_cksum.rs
@@ -627,6 +627,24 @@ fn test_check_sha2_tagged_missing_hint() {
         .stderr_contains("no properly formatted checksum lines found");
 }
 
+#[test]
+fn test_check_tagged_missing_algo() {
+    // When checking tagged lines, if the algorithm is missing, raise "improperly
+    // formatted" rather than a failed check.
+
+    let (at, mut ucmd) = at_and_ucmd!();
+    at.touch("a");
+
+    let invalid1 = "(a) = d14a028c2a3a2bc9476102bb288234c415a2b01f828ea62ac5b3e42f";
+    let invalid2 = "a) = d14a028c2a3a2bc9476102bb288234c415a2b01f828ea62ac5b3e42f";
+    let invalid3 = "(a = d14a028c2a3a2bc9476102bb288234c415a2b01f828ea62ac5b3e42f";
+
+    ucmd.arg("-c")
+        .pipe_in(format!("{invalid1}\n{invalid2}\n{invalid3}"))
+        .fails()
+        .stderr_contains("no properly formatted checksum lines found");
+}
+
 #[rstest]
 #[case::md5("md5", "d41d8cd98f00b204e9800998ecf8427e")]
 #[case::sha1("sha1", "da39a3ee5e6b4b0d3255bfef95601890afd80709")]