--- a/clear_cmd.c	Sun Aug 20 21:53:56 2006 +0000
+++ b/clear_cmd.c	Mon Aug 21 09:22:44 2006 +0000
@@ -680,7 +680,7 @@
 				SetClearCounter(tile, 0);
 			}
 
-			if (GetIndustryIndexOfField(tile) == INVALID_INDUSTRY) {
+			if (GetIndustryIndexOfField(tile) == INVALID_INDUSTRY && GetFieldType(tile) >= 7) {
 				/* This farmfield is no longer farmfield, so make it grass again */
 				MakeClear(tile, CLEAR_GRASS, 0);
 			} else {