diff --git a/harbour/include/hbextern.ch b/harbour/include/hbextern.ch
index 5530eb8600..c8c07ac030 100644
--- a/harbour/include/hbextern.ch
+++ b/harbour/include/hbextern.ch
@@ -834,8 +834,10 @@ EXTERNAL __CAPTION
 EXTERNAL __GUICOLOR
 EXTERNAL __CAPLENGTH
 EXTERNAL __CAPMETRICS
+#ifdef HB_C52_UNDOC
 EXTERNAL __MICOLUMN
 EXTERNAL __MIROW
+#endif
 EXTERNAL _ISGRAPHIC
 EXTERNAL _SETVIDEOMODE
 EXTERNAL _CHECKBOX_