diff --git a/src/map.c b/src/map.c
index b98b5a7..a8478ca 100644
--- a/src/map.c
+++ b/src/map.c
@@ -108,6 +108,14 @@ static void map_update(void) {
 
   sys = &systems_stack[map_selected];
 
+  if(!sys_isKnown(sys)) { /* System isn't known. Erase all. */
+    window_modifyText(map_wid, "txtSysname", "Unknown");
+    window_modifyText(map_wid, "txtFaction", "Unknown");
+    window_modifyText(map_wid, "txtPlanets", "Unknown");
+    return;
+  }
+
+  /* System is known. */
   window_modifyText(map_wid, "txtSysname", sys->name);
 
   if(sys->nplanets == 0)