diff --git a/openmp/libomptarget/src/omptarget.cpp b/openmp/libomptarget/src/omptarget.cpp
--- a/openmp/libomptarget/src/omptarget.cpp
+++ b/openmp/libomptarget/src/omptarget.cpp
@@ -927,6 +927,19 @@
     return OFFLOAD_FAIL;
   }
 
+  // This synchronization makes sure that before we deallocate any memory, the
+  // kernel has already finished. Otherwise, data will be freed when they're
+  // still being used.
+  // TODO: If we can separate the memory free and data transfer, we can avoid
+  // this synchronization.
+  if (Device.RTL->synchronize) {
+    rc = Device.RTL->synchronize(device_id, &AsyncInfo);
+    if (rc != OFFLOAD_SUCCESS) {
+      DP("Failed to synchronize.\n");
+      return OFFLOAD_FAIL;
+    }
+  }
+
   // Deallocate (first-)private arrays
   for (auto it : fpArrays) {
     int rt = Device.RTL->data_delete(Device.RTLDeviceID, it);
@@ -944,6 +957,8 @@
     return OFFLOAD_FAIL;
   }
 
+  // This synchronization makes sure that all data transfer have been done
+  // before returning from this function.
   if (Device.RTL->synchronize)
     return Device.RTL->synchronize(device_id, &AsyncInfo);