diff --git a/HISTORY b/HISTORY
index 19eddc0..b380d94 100755
--- a/HISTORY
+++ b/HISTORY
@@ -1,3 +1,6 @@
+May. 9 2018
+Fixed a crash bug in invalid conditional expression with class member, thanks to AaBc for pointing it out
+
 Apr. 20 2018
 Avoided a warning when a C++ compiler refers char to unsigned
 
diff --git a/core/my_basic.c b/core/my_basic.c
index ceac94b..a7bdfc0 100755
--- a/core/my_basic.c
+++ b/core/my_basic.c
@@ -8404,6 +8404,12 @@ static int _clone_clsss_field(void* data, void* extra, void* n) {
 
 			ret = _duplicate_parameter(var, 0, instance->scope);
 			_clone_object(instance->ref.s, obj, ret->data.variable->data, false, var->data->type != _DT_CLASS);
+#ifdef MB_ENABLE_SOURCE_TRACE
+			ret->source_pos = -1;
+			ret->source_row = ret->source_col = 0xFFFF;
+#else /* MB_ENABLE_SOURCE_TRACE */
+			ret->source_pos = -1;
+#endif /* MB_ENABLE_SOURCE_TRACE */
 		}
 
 		break;