diff --git a/src/io_threads.c b/src/io_threads.c
index 95d5895d0..c9345d72e 100644
--- a/src/io_threads.c
+++ b/src/io_threads.c
@@ -164,9 +164,9 @@ void waitForClientIO(client *c) {
 void adjustIOThreadsByEventLoad(int numevents, int increase_only) {
     if (server.io_threads_num == 1) return; /* All I/O is being done by the main thread. */
     debugServerAssertWithInfo(NULL, NULL, server.io_threads_num > 1);
-
-    int target_threads =
-        server.events_per_io_thread == 0 ? server.io_threads_num : numevents / server.events_per_io_thread;
+    /* When events_per_io_thread is set to 0, we offload all events to the IO threads.
+     * This is used mainly for testing purposes. */
+    int target_threads = server.events_per_io_thread == 0 ? (numevents + 1) : numevents / server.events_per_io_thread;
 
     target_threads = max(1, min(target_threads, server.io_threads_num));