diff --git a/include/teqp/json_tools.hpp b/include/teqp/json_tools.hpp
index 5647b6a2..5f49295d 100644
--- a/include/teqp/json_tools.hpp
+++ b/include/teqp/json_tools.hpp
@@ -74,7 +74,7 @@ namespace teqp{
      3. A JSON-encoded string
      
      */
-    inline auto multilevel_JSON_load(const nlohmann::json &j, const std::optional<std::string>& default_path){
+    inline auto multilevel_JSON_load(const nlohmann::json &j, const std::optional<std::string>& default_path = std::nullopt){
         
         auto is_valid_path = [](const std::string & s){
             try{
diff --git a/include/teqp/models/multifluid.hpp b/include/teqp/models/multifluid.hpp
index 1dcefbfa..4c5ca9d9 100644
--- a/include/teqp/models/multifluid.hpp
+++ b/include/teqp/models/multifluid.hpp
@@ -1039,8 +1039,43 @@ inline auto multifluidfactory(const nlohmann::json& spec) {
         nlohmann::json depcollection = nlohmann::json::array();
         if (components.size() > 1){
             BIPcollection = multilevel_JSON_load(spec.at("BIP"), root + "/dev/mixtures/mixture_binary_pairs.json");
+            
             if (spec.contains("departure")){
-                depcollection = multilevel_JSON_load(spec.at("departure"), root + "/dev/mixtures/mixture_departure_functions.json");
+                std::string msg = "departure was provided but is invalid; options are non-empty array, path to file as string, or JSON data encoded as string";
+                auto load_departure = [&msg](const nlohmann::json& j){
+                    if (j.is_array() && j.size() > 0){
+                        return j;
+                    }
+                    else if (j.is_string()){
+                        const std::string& s = j;
+                        if (s.find("PATH::") == 0){
+                            load_a_JSON_file(s.substr(6, s.size()-6));
+                        }
+                        else{
+                            try{
+                                try{
+                                    return multilevel_JSON_load(s);
+                                }
+                                catch(...){
+                                    return nlohmann::json::parse(s);
+                                }
+                            }
+                            catch(...){
+                                throw teqp::InvalidArgument(msg);
+                            }
+                        }
+                    }
+                    else{
+                        throw teqp::InvalidArgument(msg);
+                    }
+                };
+                
+                if (root.empty()){
+                    depcollection = load_departure(spec.at("departure"));
+                }
+                else{
+                    depcollection = multilevel_JSON_load(spec.at("departure"), root + "/dev/mixtures/mixture_departure_functions.json");
+                }
             }
         }
            
diff --git a/src/tests/catch_test_multifluid_RPinterop.cxx b/src/tests/catch_test_multifluid_RPinterop.cxx
index 9ebdc1a4..c9167261 100644
--- a/src/tests/catch_test_multifluid_RPinterop.cxx
+++ b/src/tests/catch_test_multifluid_RPinterop.cxx
@@ -107,6 +107,28 @@ TEST_CASE("Check RPinterop conversion Fij instead of F in BIP", "[RPinterop]") {
     CHECK_THROWS(cppinterface::make_model(j));
 }
 
+TEST_CASE("Check RPinterop departure present but empty", "[RPinterop]") {
+    auto [BIP, DEP] = RPinterop::HMXBNCfile("../doc/source/models/HMX.BNC").make_jsons();
+    auto get_w_dep = [&](nlohmann::json dep){
+        nlohmann::json model = {
+            {"components", {
+                "FLDPATH::../doc/source/models/R152A.FLD",
+                "FLDPATH::../doc/source/models/NEWR1234YF.FLD"}},
+            {"BIP", BIP},
+            {"departure", dep}
+        };
+        nlohmann::json j = {
+            {"kind", "multifluid"},
+            {"model", model}
+        };
+        return j;
+    };
+    CHECK_THROWS(cppinterface::make_model(get_w_dep(nullptr)));
+    CHECK_THROWS(cppinterface::make_model(get_w_dep({})));
+    CHECK_NOTHROW(cppinterface::make_model(get_w_dep(DEP)));
+    CHECK_NOTHROW(cppinterface::make_model(get_w_dep(DEP.dump(1))));
+}
+
 TEST_CASE("Check RPinterop conversion with passing FLDFILE:: prefix for both fluids, specified BIP and null departure function", "[RPinterop]") {
     auto BIP = R"([{
         "hash1": "63f364b0",