diff --git a/src/uu/tr/src/operation.rs b/src/uu/tr/src/operation.rs
index c768c3e86f0..026ac96a445 100644
--- a/src/uu/tr/src/operation.rs
+++ b/src/uu/tr/src/operation.rs
@@ -36,6 +36,7 @@ pub enum BadSequence {
     ClassExceptLowerUpperInSet2,
     ClassInSet2NotMatchedBySet1,
     Set1LongerSet2EndsInClass,
+    ComplementMoreThanOneUniqueInSet2,
 }
 
 impl Display for BadSequence {
@@ -66,6 +67,9 @@ impl Display for BadSequence {
             Self::Set1LongerSet2EndsInClass => {
                 write!(f, "when translating with string1 longer than string2,\nthe latter string must not end with a character class")
             }
+            Self::ComplementMoreThanOneUniqueInSet2 => {
+                write!(f, "when translating with complemented character classes,\nstring2 must map all characters in the domain to one")
+            }
         }
     }
 }
@@ -224,7 +228,6 @@ impl Sequence {
             .count();
 
         let star_compensate_len = set1_len.saturating_sub(set2_len);
-
         //Replace CharStar with CharRepeat
         set2 = set2
             .iter()
@@ -263,6 +266,21 @@ impl Sequence {
             .filter_map(to_u8)
             .collect();
 
+        // Calculate the set of unique characters in set2
+        let mut set2_uniques = set2_solved.clone();
+        set2_uniques.sort();
+        set2_uniques.dedup();
+
+        //If the complement flag is used in translate mode, only one unique character may appear in
+        //set2. Validate this with the set of uniques in set2 that we just generated.
+        if set1.iter().any(|x| matches!(x, Self::Class(_)))
+            && translating
+            && complement_flag
+            && set2_uniques.len() > 1
+        {
+            return Err(BadSequence::ComplementMoreThanOneUniqueInSet2);
+        }
+
         if set2_solved.len() < set1_solved.len()
             && !truncate_set1_flag
             && matches!(
diff --git a/tests/by-util/test_tr.rs b/tests/by-util/test_tr.rs
index a68a793bc24..4179e21fbea 100644
--- a/tests/by-util/test_tr.rs
+++ b/tests/by-util/test_tr.rs
@@ -1386,3 +1386,23 @@ fn check_set1_longer_set2_ends_in_class_with_trunc() {
         .args(&["-t", "[:lower:]a", "[:upper:]"])
         .succeeds();
 }
+
+#[test]
+fn check_complement_2_unique_in_set2() {
+    let x226 = "x".repeat(226);
+
+    // [y*] is expanded tp "y" here
+    let arg = x226 + "[y*]xxx";
+    new_ucmd!().args(&["-c", "[:upper:]", arg.as_str()]).fails();
+}
+
+#[test]
+fn check_complement_1_unique_in_set2() {
+    let x226 = "x".repeat(226);
+
+    // [y*] is expanded to "" here
+    let arg = x226 + "[y*]xxxx";
+    new_ucmd!()
+        .args(&["-c", "[:upper:]", arg.as_str()])
+        .succeeds();
+}