diff --git a/src/faction.cpp b/src/faction.cpp
index 88755156ceb65..58203db0f22e2 100644
--- a/src/faction.cpp
+++ b/src/faction.cpp
@@ -113,7 +113,7 @@ faction_template::faction_template( const JsonObject &jsobj )
     }
     lone_wolf_faction = jsobj.get_bool( "lone_wolf_faction", false );
     load_relations( jsobj );
-    mon_faction = jsobj.get_string( "mon_faction", "human" );
+    mon_faction = mfaction_str_id( jsobj.get_string( "mon_faction", "human" ) );
     for( const JsonObject jao : jsobj.get_array( "epilogues" ) ) {
         epilogue_data.emplace( jao.get_int( "power_min", std::numeric_limits<int>::min() ),
                                jao.get_int( "power_max", std::numeric_limits<int>::max() ),
diff --git a/src/faction.h b/src/faction.h
index 7cccd9f122163..0521f2eb20b1c 100644
--- a/src/faction.h
+++ b/src/faction.h
@@ -89,7 +89,7 @@ class faction_template
         bool lone_wolf_faction; // is this a faction for just one person?
         itype_id currency; // id of the faction currency
         std::map<std::string, std::bitset<npc_factions::rel_types>> relations;
-        std::string mon_faction; // mon_faction_id of the monster faction; defaults to human
+        mfaction_str_id mon_faction; // mon_faction_id of the monster faction; defaults to human
         std::set<std::tuple<int, int, snippet_id>> epilogue_data;
 };
 
diff --git a/src/npc.cpp b/src/npc.cpp
index a6ac6b3df588b..1d549475e7cc3 100644
--- a/src/npc.cpp
+++ b/src/npc.cpp
@@ -2959,9 +2959,8 @@ std::set<tripoint> npc::get_path_avoid() const
 mfaction_id npc::get_monster_faction() const
 {
     if( my_fac ) {
-        string_id<monfaction> my_mon_fac = string_id<monfaction>( my_fac->mon_faction );
-        if( my_mon_fac.is_valid() ) {
-            return my_mon_fac;
+        if( my_fac->mon_faction.is_valid() ) {
+            return my_fac->mon_faction;
         }
     }