diff --git a/reftable/stack.c b/reftable/stack.c
index 1ce4d90cb8..af0f94d882 100644
--- a/reftable/stack.c
+++ b/reftable/stack.c
@@ -579,9 +579,11 @@ out:
 	return err;
 }
 
-/* -1 = error
- 0 = up to date
- 1 = changed. */
+/*
+ * Check whether the given stack is up-to-date with what we have in memory.
+ * Returns 0 if so, 1 if the stack is out-of-date or a negative error code
+ * otherwise.
+ */
 static int stack_uptodate(struct reftable_stack *st)
 {
 	char **names = NULL;
@@ -850,10 +852,13 @@ int reftable_addition_commit(struct reftable_addition *add)
 		 * control. It is possible that a concurrent writer is already
 		 * trying to compact parts of the stack, which would lead to a
 		 * `REFTABLE_LOCK_ERROR` because parts of the stack are locked
-		 * already. This is a benign error though, so we ignore it.
+		 * already. Similarly, the stack may have been rewritten by a
+		 * concurrent writer, which causes `REFTABLE_OUTDATED_ERROR`.
+		 * Both of these errors are benign, so we simply ignore them.
 		 */
 		err = reftable_stack_auto_compact(add->stack);
-		if (err < 0 && err != REFTABLE_LOCK_ERROR)
+		if (err < 0 && err != REFTABLE_LOCK_ERROR &&
+		    err != REFTABLE_OUTDATED_ERROR)
 			goto done;
 		err = 0;
 	}
@@ -1215,9 +1220,24 @@ static int stack_compact_range(struct reftable_stack *st,
 		goto done;
 	}
 
+	/*
+	 * Check whether the stack is up-to-date. We unfortunately cannot
+	 * handle the situation gracefully in case it's _not_ up-to-date
+	 * because the range of tables that the user has requested us to
+	 * compact may have been changed. So instead we abort.
+	 *
+	 * We could in theory improve the situation by having the caller not
+	 * pass in a range, but instead the list of tables to compact. If so,
+	 * we could check that relevant tables still exist. But for now it's
+	 * good enough to just abort.
+	 */
 	err = stack_uptodate(st);
-	if (err)
+	if (err < 0)
 		goto done;
+	if (err > 0) {
+		err = REFTABLE_OUTDATED_ERROR;
+		goto done;
+	}
 
 	/*
 	 * Lock all tables in the user-provided range. This is the slice of our