diff --git a/docs/runtime/04_known_issues.md b/docs/runtime/04_known_issues.md
index 4389a6bd4f015a6579d0778c04bda549741cfcb1..25f0a616e6c4ee507db8b6ecb75c2c14f12302b1 100644
--- a/docs/runtime/04_known_issues.md
+++ b/docs/runtime/04_known_issues.md
@@ -30,6 +30,8 @@ The current implementation of Reowolf has the following known issues:
 
 - The TCP listener component should probably do a `shutdown` before a `close` on the socket handle. It should also set the `SO_REUSEADDR` option.
 
+- The TCP listener and TCP sender components have not been tested extensively in a multi-threaded setup.
+
 - The way in which putting ports are ordered to block if the corresponding getter port's main inbox is full is rather silly. This led to the introduction of the "backup inbox" as it is found in the runtime's code. There is a design decision to make here, but the current implementation is a bit silly. There are two options: (a) have an atomic boolean indicating if the message slot for an inbox is full, or (b) do away with the "main inbox" alltogether, and have an unbounded message queue.
 
 - For practical use in components whose code supports an arbitrary number of peers (i.e. their code contains an array of ports that is used for communication and changes in size during the component's lifetime), the `select` statement somehow needs to support waiting on any one of those ports.