diff --git a/src/Main.cc b/src/Main.cc
index ffc61230..0a3c9554 100644
--- a/src/Main.cc
+++ b/src/Main.cc
@@ -1605,7 +1605,7 @@ Action a_cat_client(
 
 Action a_convert_rare_item_set(
     "convert-rare-item-set", "\
-  convert-rare-item-set INPUT-FILENAME [OUTPUT-FILENAME]\n\
+  convert-rare-item-set INPUT-FILENAME [OUTPUT-FILENAME] [OPTIONS]\n\
     If OUTPUT-FILENAME is not given, print the contents of a rare item table in\n\
     a human-readable format. Otherwise, convert the input rare item set to a\n\
     different format and write it to OUTPUT-FILENAME. Both filenames must end\n\
@@ -1614,10 +1614,13 @@ Action a_convert_rare_item_set(
       .gsl (PSO BB little-endian GSL archive)\n\
       .gslb (PSO GC big-endian GSL archive)\n\
       .afs (PSO V2 little-endian AFS archive)\n\
-      .rel (Schtserv rare table; cannot be used in output filename)\n",
+      .rel (Schtserv rare table; cannot be used in output filename)\n\
+    If the --multiply=X option is given, multiplies all drop rates by X (given\n\
+    as a decimal value).\n",
     +[](Arguments& args) {
       auto version = get_cli_version(args);
 
+      double rate_factor = args.get<double>("multiply");
       auto s = make_shared<ServerState>("system/config.json");
       s->load_config_early();
       s->load_patch_indexes(false);
@@ -1646,6 +1649,10 @@ Action a_convert_rare_item_set(
         throw runtime_error("cannot determine input format; use a filename ending with .json, .gsl, .gslb, .afs, or .rel");
       }
 
+      if (rate_factor != 1.0) {
+        rs->multiply_all_rates(rate_factor);
+      }
+
       string output_filename = args.get<string>(2, false);
       if (output_filename.empty() || (output_filename == "-")) {
         rs->print_all_collections(stdout, s->item_name_index(version));
diff --git a/src/RareItemSet.cc b/src/RareItemSet.cc
index c90c3269..8ea0720e 100644
--- a/src/RareItemSet.cc
+++ b/src/RareItemSet.cc
@@ -509,6 +509,21 @@ JSON RareItemSet::json(shared_ptr<const ItemNameIndex> name_index) const {
   return modes_dict;
 }
 
+void RareItemSet::multiply_all_rates(double factor) {
+  auto multiply_rates_vec = +[](vector<vector<ExpandedDrop>>& vec, double factor) -> void {
+    for (auto& vec_it : vec) {
+      for (auto& z_it : vec_it) {
+        uint64_t new_probability = z_it.probability * factor;
+        z_it.probability = min<uint64_t>(new_probability, 0xFFFFFFFF);
+      }
+    }
+  };
+  for (auto& coll_it : this->collections) {
+    multiply_rates_vec(coll_it.second.rt_index_to_specs, factor);
+    multiply_rates_vec(coll_it.second.box_area_to_specs, factor);
+  }
+}
+
 void RareItemSet::print_collection(
     FILE* stream,
     GameMode mode,
diff --git a/src/RareItemSet.hh b/src/RareItemSet.hh
index aace5c9c..bc746cc4 100644
--- a/src/RareItemSet.hh
+++ b/src/RareItemSet.hh
@@ -39,6 +39,8 @@ public:
   std::string serialize_gsl(bool big_endian) const;
   JSON json(std::shared_ptr<const ItemNameIndex> name_index = nullptr) const;
 
+  void multiply_all_rates(double factor);
+
   void print_collection(
       FILE* stream,
       GameMode mode,