diff --git a/lib_fiber/cpp/src/wait_group.cpp b/lib_fiber/cpp/src/wait_group.cpp
index d102e3c6f..6324b79ca 100644
--- a/lib_fiber/cpp/src/wait_group.cpp
+++ b/lib_fiber/cpp/src/wait_group.cpp
@@ -17,8 +17,7 @@ wait_group::~wait_group(void)
 
 void wait_group::add(int n)
 {
-    state_ += (long long)n << 32;
-    long long state = state_;
+    long long state = state_.add_fetch((long long)n << 32);
     int c = (int)(state >> 32);
     uint32_t w =  (uint32_t)state;
     if(c < 0){
@@ -52,22 +51,26 @@ void wait_group::done(void)
 
 void wait_group::wait(void)
 {
-    long long state = state_;
-    int c = (int)(state >> 32);
-    uint32_t w =  (uint32_t)state;
-    if(c == 0) return;
-    state_++;
-    bool found;
+    for(;;){
+        long long state = state_;
+        int c = (int)(state >> 32);
+        uint32_t w =  (uint32_t)state;
+        if(c == 0) return;
+        if(state_.cas(state, state + 1) == state){
+            bool found;
 #ifdef	_DEBUG
-    unsigned long* tid = box_->pop(-1, &found);
-    assert(found);
-    delete tid;
+            unsigned long* tid = box_->pop(-1, &found);
+            assert(found);
+            delete tid;
 #else
-    (void) box_->pop(-1, &found);
-    assert(found);
+            (void) box_->pop(-1, &found);
+            assert(found);
 #endif
-    if(state_ != 0){
-        acl_msg_fatal("wait_group: wait_group is reused before previous wait has returned");
+            if(state_ != 0){
+                acl_msg_fatal("wait_group: wait_group is reused before previous wait has returned");
+            }
+            return;
+        }
     }
 }