diff --git a/crates/engine/src/units.rs b/crates/engine/src/units.rs
index 83c115316..5575273ca 100644
--- a/crates/engine/src/units.rs
+++ b/crates/engine/src/units.rs
@@ -142,6 +142,9 @@ pub fn parse_distance(s: &str) -> Option<f64> {
         Some(r) => (true, r.trim()),
         None => (false, t),
     };
+    if neg && t.starts_with(['-', '+']) {
+        return None;
+    }
     let mut total = 0.0;
     let mut rest = t;
     let mut parsed = false;
@@ -430,6 +433,14 @@ mod tests {
         assert_eq!(parse_distance(""), None);
     }
 
+    #[test]
+    fn parse_distance_rejects_doubled_minus() {
+        assert_eq!(parse_distance("--5"), None);
+        assert_eq!(parse_distance("- -3/4"), None);
+        assert_eq!(parse_distance("-5"), Some(-5.0));
+        assert_eq!(parse_distance("-3/4"), Some(-0.75));
+    }
+
     #[test]
     fn parse_distance_needs_a_number() {
         assert_eq!(parse_distance("-"), None);