diff --git a/game/game/compatibility/cpu32.cpp b/game/game/compatibility/cpu32.cpp
index c5f9a5fdf..c41bcf6be 100644
--- a/game/game/compatibility/cpu32.cpp
+++ b/game/game/compatibility/cpu32.cpp
@@ -255,7 +255,7 @@ void Cpu32::callFunction(ptr32_t func) {
 
 std::string Cpu32::popString() {
   if(stack.size()==0)
-    return 0;
+    return "";
   auto ptr = stack.back();
   stack.pop_back();
 
diff --git a/game/graphics/instancestorage.cpp b/game/graphics/instancestorage.cpp
index 40c79398a..be52ee868 100644
--- a/game/graphics/instancestorage.cpp
+++ b/game/graphics/instancestorage.cpp
@@ -207,11 +207,10 @@ bool InstanceStorage::commit(Encoder<CommandBuffer>& cmd, uint8_t fId) {
   }
 
 void InstanceStorage::join() {
-  while(true) {
-    std::unique_lock<std::mutex> lck(sync);
-    if(uploadFId<0)
-      break;
-    }
+  std::unique_lock<std::mutex> lck(sync);
+  uploadCnd.wait(lck, [this] {
+    return uploadFId < 0;
+    });
   }
 
 InstanceStorage::Id InstanceStorage::alloc(const size_t size) {
@@ -307,13 +306,15 @@ void InstanceStorage::uploadMain() {
   Workers::setThreadName("InstanceStorage upload");
   while(true) {
     std::unique_lock<std::mutex> lck(sync);
-    uploadCnd.wait(lck);
+    uploadCnd.wait(lck, [this] {
+      return uploadFId >= 0;
+      });
     if(uploadFId==Resources::MaxFramesInFlight)
       break;
-    if(uploadFId<0)
-      continue;
 
     patchGpu[uploadFId].update(patchCpu);
     uploadFId = -1;
+    lck.unlock();
+    uploadCnd.notify_all();
     }
   }