Index: uspace/lib/c/generic/async/client.c
===================================================================
--- uspace/lib/c/generic/async/client.c	(revision b42fa76a0c3b8f4712aef6f5b0299f902ceb1917)
+++ uspace/lib/c/generic/async/client.c	(revision 698ce34cc9b363bc132f831055a497f5ea229942)
@@ -1069,9 +1069,5 @@
 
 	fibril_mutex_lock(&async_sess_mutex);
-
-	if (sess->exchanges > 0) {
-		fibril_mutex_unlock(&async_sess_mutex);
-		return EBUSY;
-	}
+	assert(sess->exchanges == 0);
 
 	errno_t rc = async_hangup_internal(sess->phone);