diff --git a/src/gmtool.c b/src/gmtool.c
index 1fba47be6..bfe7cbe25 100644
--- a/src/gmtool.c
+++ b/src/gmtool.c
@@ -565,7 +565,9 @@ static void terraform_at(coordinate * c, const terrain_type * terrain)
         if (r == NULL) {
             r = new_region(nx, ny, c->pl, 0);
         }
-        terraform_region(r, terrain);
+        if (!(r->units && fval(r->terrain, LAND_REGION) && !fval(terrain, LAND_REGION))) {
+            terraform_region(r, terrain);
+        }
     }
 }
 
@@ -589,7 +591,9 @@ terraform_selection(selection * selected, const terrain_type * terrain)
             if (r == NULL) {
                 r = new_region(nx, ny, pl, 0);
             }
-            terraform_region(r, terrain);
+            if (!(r->units && fval(r->terrain, LAND_REGION) && !fval(terrain, LAND_REGION))) {
+                terraform_region(r, terrain);
+            }
             tp = &t->nexthash;
         }
     }
diff --git a/src/kernel/region.c b/src/kernel/region.c
index 27936c79f..7ce757043 100644
--- a/src/kernel/region.c
+++ b/src/kernel/region.c
@@ -1060,10 +1060,6 @@ void terraform_region(region * r, const terrain_type * terrain)
     rawmaterial **lrm = &r->resources;
 
     assert(terrain);
-    if (r->units && fval(r->terrain, LAND_REGION) && !fval(terrain, LAND_REGION)) {
-        log_error("region %s contains units, not terraforming it to %s.", regionname(r, NULL), terrain->_name);
-        return;
-    }
     while (*lrm) {
         rawmaterial *rm = *lrm;
         const resource_type *rtype = NULL;