diff --git a/lib/src/cnf/mod.rs b/lib/src/cnf/mod.rs
index d05304b0..c29d158c 100644
--- a/lib/src/cnf/mod.rs
+++ b/lib/src/cnf/mod.rs
@@ -1,4 +1,5 @@
 // Specifies how many concurrent jobs can be buffered in the worker channel.
+#[cfg(feature = "parallel")]
 pub const MAX_CONCURRENT_TASKS: usize = 64;
 
 // Specifies how many subqueries will be processed recursively before the query fails.