diff --git a/src/iomux.c b/src/iomux.c
index c648ae6..ffa9cfe 100644
--- a/src/iomux.c
+++ b/src/iomux.c
@@ -907,6 +907,33 @@ int iomux_num_fds(iomux_t *iomux)
     return num_fds;
 }
 
+int
+iomux_set_output_callback(iomux_t *iomux, int fd, iomux_output_callback_t cb)
+{
+    MUTEX_LOCK(iomux);
+    if (!iomux->connections[fd]) {
+        MUTEX_UNLOCK(iomux);
+        return 0;
+    }
+    iomux->connections[fd]->cbs.mux_output = cb;
+    MUTEX_UNLOCK(iomux);
+    return 1;
+}
+
+int
+iomux_unset_output_callback(iomux_t *iomux, int fd)
+{
+    MUTEX_LOCK(iomux);
+    if (!iomux->connections[fd]) {
+        MUTEX_UNLOCK(iomux);
+        return 0;
+    }
+    iomux_output_callback_t prev = iomux->connections[fd]->cbs.mux_output;
+    iomux->connections[fd]->cbs.mux_output = NULL;
+    MUTEX_UNLOCK(iomux);
+    return prev ? 1 : 0;
+}
+
 #if defined(HAVE_KQUEUE)
 void
 iomux_run(iomux_t *iomux, struct timeval *tv_default)
diff --git a/src/iomux.h b/src/iomux.h
index 5cd8bbb..e9aad4b 100644
--- a/src/iomux.h
+++ b/src/iomux.h
@@ -268,6 +268,9 @@ void iomux_run(iomux_t *iomux, struct timeval *timeout);
  */
 int iomux_write(iomux_t *iomux, int fd, const void *buf, int len);
 
+int iomux_set_output_callback(iomux_t *iomux, int fd, iomux_output_callback_t cb);
+int iomux_unset_output_callback(iomux_t *iomux, int fd);
+
 /**
  * @brief Close a file handled by the iomux
  * @param iomux A valid iomux handler