diff --git a/src/space.c b/src/space.c
index 95d8a32..49c71d5 100644
--- a/src/space.c
+++ b/src/space.c
@@ -1008,7 +1008,8 @@ int space_sysLoad(xmlNodePtr parent) {
       do {
         if(xml_isNode(cur, "known")) {
           sys = system_get(xml_get(cur));
-          sys_setFlag(sys, SYSTEM_KNOWN);
+          if(sys != NULL) /* Must exist. */
+            sys_setFlag(sys, SYSTEM_KNOWN);
         }
       } while(xml_nextNode(cur));
     }