diff --git a/tokio/src/runtime/builder.rs b/tokio/src/runtime/builder.rs
index f4bf3a259..5b7130e74 100644
--- a/tokio/src/runtime/builder.rs
+++ b/tokio/src/runtime/builder.rs
@@ -445,6 +445,15 @@ impl Builder {
     ///
     /// The default value is 512.
     ///
+    /// # Queue Behavior
+    ///
+    /// When a blocking task is submitted, it will be inserted into a queue. If available, one of
+    /// the idle threads will be notified to run the task. Otherwise, if the threshold set by this
+    /// method has not been reached, a new thread will be spawned. If no idle thread is available
+    /// and no more threads are allowed to be spawned, the task will remain in the queue until one
+    /// of the busy threads pick it up. Note that since the queue does not apply any backpressure,
+    /// it could potentially grow unbounded.
+    ///
     /// # Panics
     ///
     /// This will panic if `val` is not larger than `0`.