diff --git a/src/c/symbols_list.h b/src/c/symbols_list.h
index c46ad787b..92361f796 100755
--- a/src/c/symbols_list.h
+++ b/src/c/symbols_list.h
@@ -1640,8 +1640,9 @@ cl_symbols[] = {
 {MP_ "SEMAPHORE" ECL_FUN(NULL, NULL, -1) ECL_VAR(MP_ORDINARY, OBJNULL)},
 {MP_ "MAKE-SEMAPHORE" ECL_FUN("mp_make_semaphore", IF_MP(mp_make_semaphore), -1) ECL_VAR(MP_ORDINARY, OBJNULL)},
 {MP_ "SIGNAL-SEMAPHORE" ECL_FUN("mp_signal_semaphore", IF_MP(mp_signal_semaphore), -2) ECL_VAR(MP_ORDINARY, OBJNULL)},
-{MP_ "WAIT-ON-SEMAPHORE" ECL_FUN("mp_wait_on_semaphore", IF_MP(mp_wait_on_semaphore), 1) ECL_VAR(MP_ORDINARY, OBJNULL)},
-{MP_ "TRY-GET-SEMAPHORE" ECL_FUN("mp_try_get_semaphore", IF_MP(mp_try_get_semaphore), 1) ECL_VAR(MP_ORDINARY, OBJNULL)},
+{MP_ "SEMAPHORE-WAIT" ECL_FUN("mp_semaphore_wait", IF_MP(mp_semaphore_wait), 3) ECL_VAR(MP_ORDINARY, OBJNULL)},
+{MP_ "WAIT-ON-SEMAPHORE" ECL_FUN("mp_wait_on_semaphore", IF_MP(mp_wait_on_semaphore), -2) ECL_VAR(MP_ORDINARY, OBJNULL)},
+{MP_ "TRY-GET-SEMAPHORE" ECL_FUN("mp_try_get_semaphore", IF_MP(mp_try_get_semaphore), -2) ECL_VAR(MP_ORDINARY, OBJNULL)},
 {MP_ "SEMAPHORE-COUNT" ECL_FUN("mp_semaphore_count", IF_MP(mp_semaphore_count), 1) ECL_VAR(MP_ORDINARY, OBJNULL)},
 {MP_ "SEMAPHORE-NAME" ECL_FUN("mp_semaphore_name", IF_MP(mp_semaphore_name), 1) ECL_VAR(MP_ORDINARY, OBJNULL)},
 {MP_ "SEMAPHORE-WAIT-COUNT" ECL_FUN("mp_semaphore_wait_count", IF_MP(mp_semaphore_wait_count), 1) ECL_VAR(MP_ORDINARY, OBJNULL)},
diff --git a/src/c/threads/semaphore.d b/src/c/threads/semaphore.d
index 86c191ca8..69f32dbbb 100644
--- a/src/c/threads/semaphore.d
+++ b/src/c/threads/semaphore.d
@@ -82,31 +82,67 @@ mp_semaphore_wait_count(cl_object semaphore)
     @(return);
   } @)
 
+static inline void
+semaphore_wait_unprotected(cl_object semaphore, cl_object count, cl_object timeout)
+{
+  int rc;
+  cl_env_ptr the_env = ecl_process_env();
+  cl_fixnum counter = fixnnint(count);
+  ecl_mutex_t *mutex = &semaphore->semaphore.mutex;
+  ecl_cond_var_t *cv = &semaphore->semaphore.cv;
+  if (timeout == ECL_NIL) {
+    do {
+      ecl_setq(the_env, ECL_INTERRUPTS_ENABLED, ECL_T);
+      ecl_cond_var_wait(cv, mutex);
+      ecl_setq(the_env, ECL_INTERRUPTS_ENABLED, ECL_NIL);
+    } while (semaphore->semaphore.counter < counter);
+  } else {
+    cl_object deadline = ecl_plus(cl_get_internal_real_time(),
+                                  ecl_times(timeout, ecl_make_fixnum(1000)));
+    double seconds = ecl_to_double(timeout);
+    do {
+      ecl_setq(the_env, ECL_INTERRUPTS_ENABLED, ECL_T);
+      rc = ecl_cond_var_timedwait(cv, mutex, seconds);
+      ecl_setq(the_env, ECL_INTERRUPTS_ENABLED, ECL_NIL);
+      timeout = ecl_minus(deadline, cl_get_internal_real_time());
+      seconds = ecl_to_double(timeout);
+    } while(semaphore->semaphore.counter < counter
+            && rc != ECL_MUTEX_TIMEOUT
+            && seconds >= 0);
+  }
+}
+
 cl_object
-mp_wait_on_semaphore(cl_object semaphore)
+mp_semaphore_wait(cl_object semaphore, cl_object count, cl_object timeout)
 {
   cl_env_ptr the_env = ecl_process_env();
+  cl_fixnum counter = fixnnint(count);
   volatile cl_object output;
   unlikely_if (ecl_t_of(semaphore) != t_semaphore) {
-    FEwrong_type_only_arg(@[mp::wait-on-semaphore], semaphore, @[mp::semaphore]);
+    FEwrong_type_only_arg(@[mp::semaphore-wait], semaphore, @[mp::semaphore]);
   }
   ecl_bds_bind(the_env, ECL_INTERRUPTS_ENABLED, ECL_NIL);
   ecl_mutex_lock(&semaphore->semaphore.mutex);
-  if (semaphore->semaphore.counter == 0) {
+  if (semaphore->semaphore.counter >= counter) {
+    output = ecl_make_fixnum(semaphore->semaphore.counter);
+    semaphore->semaphore.counter -= counter;
+    ecl_mutex_unlock(&semaphore->semaphore.mutex);
+  } else if (timeout == ECL_NIL || ecl_plusp(timeout)) {
     semaphore->semaphore.wait_count++;
     ECL_UNWIND_PROTECT_BEGIN(the_env) {
-      do {
-        ecl_setq(the_env, ECL_INTERRUPTS_ENABLED, ECL_T);
-        ecl_cond_var_wait(&semaphore->semaphore.cv, &semaphore->semaphore.mutex);
-        ecl_setq(the_env, ECL_INTERRUPTS_ENABLED, ECL_NIL);
-      } while (semaphore->semaphore.counter == 0);
-      output = ecl_make_fixnum(semaphore->semaphore.counter--);
+      semaphore_wait_unprotected(semaphore, count, timeout);
+      if (semaphore->semaphore.counter >= counter) {
+        output = ecl_make_fixnum(semaphore->semaphore.counter);
+        semaphore->semaphore.counter -= counter;
+      } else {
+        output = ECL_NIL;
+      }
     } ECL_UNWIND_PROTECT_THREAD_SAFE_EXIT {
       semaphore->semaphore.wait_count--;
       ecl_mutex_unlock(&semaphore->semaphore.mutex);
     } ECL_UNWIND_PROTECT_THREAD_SAFE_END;
   } else {
-    output = ecl_make_fixnum(semaphore->semaphore.counter--);
+    output = ECL_NIL;
     ecl_mutex_unlock(&semaphore->semaphore.mutex);
   }
   ecl_bds_unwind1(the_env);
@@ -114,23 +150,16 @@ mp_wait_on_semaphore(cl_object semaphore)
   ecl_return1(the_env, output);
 }
 
-cl_object
-mp_try_get_semaphore(cl_object semaphore)
-{
-  cl_env_ptr the_env = ecl_process_env();
-  cl_object output;
-  unlikely_if (ecl_t_of(semaphore) != t_semaphore) {
-    FEwrong_type_only_arg(@[mp::try-get-semaphore], semaphore, @[mp::semaphore]);
-  }
-  ecl_disable_interrupts_env(the_env);
-  ecl_mutex_lock(&semaphore->semaphore.mutex);
-  if (semaphore->semaphore.counter > 0) {
-    output = ecl_make_fixnum(semaphore->semaphore.counter--);
-  } else {
-    output = ECL_NIL;
-  }
-  ecl_mutex_unlock(&semaphore->semaphore.mutex);
-  ecl_enable_interrupts_env(the_env);
-  ecl_return1(the_env, output);
-}
+@(defun mp::wait-on-semaphore (semaphore &key (count ecl_make_fixnum(1))
+                                              (timeout ECL_NIL))
+  @ {
+    cl_object output = mp_semaphore_wait(semaphore, count, timeout);
+    @(return output);
+  } @)
 
+@(defun mp::try-get-semaphore (semaphore &optional (count ecl_make_fixnum(1)))
+  @ {
+    cl_object timeout = ecl_make_fixnum(0);
+    cl_object output = mp_semaphore_wait(semaphore, count, timeout);
+    @(return output);
+  } @)
diff --git a/src/cmp/proclamations.lsp b/src/cmp/proclamations.lsp
index 2a52a1eff..15a8ccfb3 100644
--- a/src/cmp/proclamations.lsp
+++ b/src/cmp/proclamations.lsp
@@ -1513,8 +1513,9 @@
 #+threads (proclamation mp:semaphore-name (mp:semaphore) t :reader)
 #+threads (proclamation mp:semaphore-count (mp:semaphore) fixnum :reader)
 #+threads (proclamation mp:semaphore-wait-count (mp:semaphore) natural :reader)
-#+threads (proclamation mp:wait-on-semaphore (mp:semaphore) fixnum)
-#+threads (proclamation mp:try-get-semaphore (mp:semaphore) t)
+#+threads (proclamation mp:semaphore-wait (mp:semaphore fixnum real) t)
+#+threads (proclamation mp:wait-on-semaphore (mp:semaphore &key) t)
+#+threads (proclamation mp:try-get-semaphore (mp:semaphore &optional fixnum) t)
 #+threads (proclamation mp:signal-semaphore (mp:semaphore &optional fixnum) t)
 
 ;;;
diff --git a/src/h/external.h b/src/h/external.h
index 4a1a8692d..8066d7827 100755
--- a/src/h/external.h
+++ b/src/h/external.h
@@ -1816,9 +1816,10 @@ extern ECL_API cl_object mp_make_semaphore _ECL_ARGS((cl_narg, ...));
 extern ECL_API cl_object mp_semaphore_count(cl_object);
 extern ECL_API cl_object mp_semaphore_name(cl_object);
 extern ECL_API cl_object mp_semaphore_wait_count(cl_object);
-extern ECL_API cl_object mp_wait_on_semaphore(cl_object);
-extern ECL_API cl_object mp_try_get_semaphore(cl_object);
-extern ECL_API cl_object mp_signal_semaphore _ECL_ARGS((cl_narg, cl_object, ...));
+extern ECL_API cl_object mp_semaphore_wait(cl_object, cl_object, cl_object);
+extern ECL_API cl_object mp_wait_on_semaphore _ECL_ARGS((cl_narg, cl_object, ...));
+extern ECL_API cl_object mp_try_get_semaphore _ECL_ARGS((cl_narg, cl_object, ...));
+extern ECL_API cl_object mp_signal_semaphore  _ECL_ARGS((cl_narg, cl_object, ...));
 extern ECL_API cl_object ecl_make_semaphore(cl_object name, cl_fixnum count);
 
 /* threads/barrier.d */