diff --git a/optframe/engine.py b/optframe/engine.py
index 3bb375e..b6acb1b 100644
--- a/optframe/engine.py
+++ b/optframe/engine.py
@@ -35,6 +35,10 @@
         print(f"Error: {libfile} not found.")
         assert False
 
+# final check on library...
+if optframe_lib is None:
+    raise ImportError(f"Error: library 'optframe_lib' not found.")
+
 FCORE_WARN_ISSUES = True
 
 # =====================================