diff --git a/akka-actor/src/main/resources/reference.conf b/akka-actor/src/main/resources/reference.conf
index 40eac6f30a2..71a95ad7645 100644
--- a/akka-actor/src/main/resources/reference.conf
+++ b/akka-actor/src/main/resources/reference.conf
@@ -360,7 +360,9 @@ akka {
         # Define a fixed thread pool size with this property. The corePoolSize
         # and the maximumPoolSize of the ThreadPoolExecutor will be set to this
         # value, if it is defined. Then the other pool-size properties will not
-        # be used.
+        # be used. 
+        # 
+        # Valid values are: `off` or a positive integer.
         fixed-pool-size = off
 
         # Min number of threads to cap factor-based corePoolSize number to