diff --git a/crates/engine/src/cf.rs b/crates/engine/src/cf.rs
index 6640c7a..9979bff 100644
--- a/crates/engine/src/cf.rs
+++ b/crates/engine/src/cf.rs
@@ -392,4 +392,18 @@ mod tests {
         // No blanks: neither the empty cell nor the one holding a space.
         assert_eq!([look("A1"), look("A2"), look("A4")].map(border), [true, false, false]);
     }
+
+    #[test]
+    fn cell_value_operator_names() {
+        let mut s = crate::Session::new();
+        s.new_workbook();
+        s.execute("range.setValues", json!({"range": "A1", "values": [[3], [7]]})).unwrap();
+        let rule = |op: &str| json!({"range": "A1:A2", "rule": {"type": "cellIs", "operator": op, "value": "5", "preset": "lightRedFill"}});
+        s.execute("home.conditionalFormat", rule("lessThan")).unwrap();
+        assert!(s.execute("home.conditionalFormat", rule("smaller")).is_err());
+        let d = s.doc().unwrap();
+        let mut cache = CfCache::new();
+        let mut look = |a: &str| cache.look(&d.wb, 0, CellRef::parse(a).unwrap()).and_then(|l| l.style).is_some();
+        assert_eq!([look("A1"), look("A2")], [true, false]);
+    }
 }
diff --git a/crates/engine/src/cmd/insert.rs b/crates/engine/src/cmd/insert.rs
index 4c96005..3fc6cff 100644
--- a/crates/engine/src/cmd/insert.rs
+++ b/crates/engine/src/cmd/insert.rs
@@ -1157,15 +1157,17 @@ fn add_cf(s: &mut Session, p: &Json) -> Result<Json> {
     };
     let rule = match kind.as_str() {
         "cellIs" => {
+            // Excel's file and VBA names (`lessThan`, …) are accepted too.
             let op = match g("operator").as_deref().unwrap_or("greater") {
                 "between" => CfOperator::Between,
                 "notBetween" => CfOperator::NotBetween,
                 "equal" => CfOperator::Equal,
                 "notEqual" => CfOperator::NotEqual,
-                "less" => CfOperator::Less,
-                "greaterOrEqual" => CfOperator::GreaterOrEqual,
-                "lessOrEqual" => CfOperator::LessOrEqual,
-                _ => CfOperator::Greater,
+                "less" | "lessThan" => CfOperator::Less,
+                "greaterOrEqual" | "greaterThanOrEqual" => CfOperator::GreaterOrEqual,
+                "lessOrEqual" | "lessThanOrEqual" => CfOperator::LessOrEqual,
+                "greater" | "greaterThan" => CfOperator::Greater,
+                other => return Err(bad("home.conditionalFormat", format!("unknown operator `{other}`"))),
             };
             let a = rule.get("value").map(super::edit::json_to_input).unwrap_or_default();
             let b = rule.get("value2").map(super::edit::json_to_input);