diff --git a/src/analyses/libraryDesc.ml b/src/analyses/libraryDesc.ml
index 597c08f72f..fde24ac77e 100644
--- a/src/analyses/libraryDesc.ml
+++ b/src/analyses/libraryDesc.ml
@@ -58,6 +58,7 @@ type special =
   | MutexAttrSetType of { attr:Cil.exp; typ: Cil.exp; }
   | MutexInit of { mutex:Cil.exp; attr: Cil.exp; }
   | SemInit of { sem: Cil.exp; pshared: Cil.exp; value: Cil.exp; }
+  | SemWait of { sem: Cil.exp; try_:bool}
   | Wait of { cond: Cil.exp; mutex: Cil.exp; }
   | TimedWait of { cond: Cil.exp; mutex: Cil.exp; abstime: Cil.exp; (** Unused *) }
   | Math of { fun_args: math; }
diff --git a/src/analyses/libraryFunctions.ml b/src/analyses/libraryFunctions.ml
index f3c00f9b48..08ec2e2b3e 100644
--- a/src/analyses/libraryFunctions.ml
+++ b/src/analyses/libraryFunctions.ml
@@ -407,7 +407,10 @@ let pthread_descs_list: (string * LibraryDesc.t) list = LibraryDsl.[
     ("sem_timedwait", unknown [drop "sem" [r]; drop "abs_timeout" [r]]); (* no write accesses to sem because sync primitive itself has no race *)
     ("pthread_setaffinity_np", unknown [drop "thread" []; drop "cpusetsize" []; drop "cpuset" [r]]);
     ("pthread_getaffinity_np", unknown [drop "thread" []; drop "cpusetsize" []; drop "cpuset" [w]]);
+    (* TODO: Remove w as soon as we have proper support for semaphores *)
     ("sem_init", special [__ "sem" [w]; __ "pshared" []; __ "value" []] @@ fun sem pshared value -> SemInit {sem; pshared; value});
+    ("sem_wait", special [__ "sem" [w]] @@ fun sem -> SemWait {sem; try_ = false});
+    ("sem_trywait", special [__ "sem" [w]] @@ fun sem -> SemWait {sem; try_ = true});
   ]
 
 (** GCC builtin functions.
@@ -1156,7 +1159,6 @@ let invalidate_actions = [
     "setrlimit", readsAll; (*safe*)
     "getrlimit", writes [2]; (*keep [2]*)
     "sem_destroy", readsAll; (*safe*)
-    "sem_wait", readsAll; (*safe*)
     "sem_post", readsAll; (*safe*)
     "PL_NewHashTable", readsAll; (*safe*)
     "assert_failed", readsAll; (*safe*)