diff --git a/src/ifcexpressparser/schema_class.py b/src/ifcexpressparser/schema_class.py
index 8ce5d9d0dd..80dd53633e 100644
--- a/src/ifcexpressparser/schema_class.py
+++ b/src/ifcexpressparser/schema_class.py
@@ -92,6 +92,7 @@ class SchemaClass(codegen.Base):
                       
         statements.append("""
 #if defined(__clang__)
+__attribute__((optnone))
 #elif defined(__GNUC__) || defined(__GNUG__)
 #pragma GCC push_options
 #pragma GCC optimize ("O0")