1 files changed, 3 insertions, 1 deletions
diff --git a/crawl-ref/source/mapdef.cc b/crawl-ref/source/mapdef.cc
index d116bd6d4c..8d9e7408af 100644
--- a/crawl-ref/source/mapdef.cc
+++ b/crawl-ref/source/mapdef.cc
@@ -3352,6 +3352,8 @@ void keyed_mapspec::parse_features(const std::string &s)
 feature_spec keyed_mapspec::parse_trap(std::string s, int weight)
 {
     strip_tag(s, "trap");
+    const bool known = strip_tag(s, "known");
+
     trim_string(s);
     lowercase(s);
 
@@ -3359,7 +3361,7 @@ feature_spec keyed_mapspec::parse_trap(std::string s, int weight)
     if (trap == -1)
         err = make_stringf("bad trap name: '%s'", s.c_str());
 
-    feature_spec fspec(-1, weight);
+    feature_spec fspec(known ? 1 : -1, weight);
     fspec.trap = trap;
     return (fspec);
 }