# UNDF: UNDF-2026-000000935
--- a/src/overmap_ui.cpp
+++ b/src/overmap_ui.cpp
@@ -1,5 +1,6 @@
 // ... (includes)
 #include <algorithm>
+#include <unordered_set>

 // In overmap_ui::search()
 // BEFORE (CWE-407): overmap_checked is std::vector with std::find for dedup
@@ -7,7 +8,7 @@
 //   radius = OMAPX * 5 = 900, iterating ~3.24M points
 //   Each std::find is O(M) where M = overmaps already checked
 //   Total: O(P * M) where P = points in radius, M = distinct overmaps
-    std::vector<point_abs_om> overmap_checked;
+    std::unordered_set<point_abs_om> overmap_checked;

     const int radius = OMAPX * 5; // arbitrary
     for( const tripoint_abs_omt &p : points_in_radius( curs, radius ) ) {
@@ -16,9 +17,8 @@
             tripoint_om_omt om_relative = om_loc.local;
             point_abs_om om_cache = project_to<coords::om>( p.xy() );

-            if( std::find( overmap_checked.begin(), overmap_checked.end(),
-                           om_cache ) == overmap_checked.end() ) {
-                overmap_checked.push_back( om_cache );
+            if( overmap_checked.find( om_cache ) == overmap_checked.end() ) {
+                overmap_checked.insert( om_cache );
                 std::vector<point_abs_omt> notes = om_loc.om->find_notes( curs.z(), term );
                 locations.insert( locations.end(), notes.begin(), notes.end() );
             }