diff --git a/src/flow/binary/bounds.rs b/src/flow/binary/bounds.rs
index 0e96553..8069798 100644
--- a/src/flow/binary/bounds.rs
+++ b/src/flow/binary/bounds.rs
@@ -10,7 +10,8 @@ pub struct Bounds<A> {
 
 pub enum BoundsError<A> {
     BoundsViolated { l: A, r: A },
-    CannotJoin(A),
+    OverflowL(A),
+    OverflowR(A),
 }
 
 impl<A: Clone> Bounds<A> {
@@ -60,12 +61,12 @@ impl<A: Clone> Bounds<A> {
         if let Some(lr) = &l.r {
             Self::ordered(lr, key, comparator)?
         } else {
-            Err(BoundsError::CannotJoin(key.clone()))?
+            Err(BoundsError::OverflowL(key.clone()))?
         }
         if let Some(rl) = &r.l {
             Self::ordered(key, rl, comparator)?
         } else {
-            Err(BoundsError::CannotJoin(key.clone()))?
+            Err(BoundsError::OverflowR(key.clone()))?
         }
         Self::new(l.l, r.r, comparator)
     }