diff --git a/jetty-util/src/main/java/org/eclipse/jetty/util/Pool.java b/jetty-util/src/main/java/org/eclipse/jetty/util/Pool.java
index 7fa2c441c98a..9a9752cad47e 100644
--- a/jetty-util/src/main/java/org/eclipse/jetty/util/Pool.java
+++ b/jetty-util/src/main/java/org/eclipse/jetty/util/Pool.java
@@ -301,6 +301,11 @@ public Entry acquire()
             {
                 LOGGER.ignore(e);
                 size = entries.size();
+                // Size can be 0 when the pool is in the middle of
+                // acquiring a connection while another thread
+                // removes the last one from the pool.
+                if (size == 0)
+                    break;
             }
             index = (index + 1) % size;
         }