diff --git a/src/auxiliary/JSON.cpp b/src/auxiliary/JSON.cpp
index 386cd438bc..168cab7bf6 100644
--- a/src/auxiliary/JSON.cpp
+++ b/src/auxiliary/JSON.cpp
@@ -249,7 +249,7 @@ namespace
         case nlohmann::json::value_t::number_unsigned:
             return val.get<nlohmann::json::number_unsigned_t>();
         case nlohmann::json::value_t::number_float:
-            return val.get<nlohmann::json::number_float_t>();
+            return (long double)val.get<nlohmann::json::number_float_t>();
         case nlohmann::json::value_t::binary:
             return val.get<nlohmann::json::binary_t>();
         case nlohmann::json::value_t::discarded:
diff --git a/src/config.cpp b/src/config.cpp
index 2b45767df1..ff1a0cb471 100644
--- a/src/config.cpp
+++ b/src/config.cpp
@@ -34,6 +34,7 @@ std::map<std::string, bool> openPMD::getVariants()
     return std::map<std::string, bool>{
         {"mpi", bool(openPMD_HAVE_MPI)},
         {"json", true},
+        {"toml", true},
         {"hdf5", bool(openPMD_HAVE_HDF5)},
         {"adios1", false},
         {"adios2", bool(openPMD_HAVE_ADIOS2)}};
@@ -43,6 +44,7 @@ std::vector<std::string> openPMD::getFileExtensions()
 {
     std::vector<std::string> fext;
     fext.emplace_back("json");
+    fext.emplace_back("toml");
 #if openPMD_HAVE_ADIOS2
     fext.emplace_back("bp");
 #endif
diff --git a/test/SerialIOTest.cpp b/test/SerialIOTest.cpp
index 71c0a9b8a3..5bac468525 100644
--- a/test/SerialIOTest.cpp
+++ b/test/SerialIOTest.cpp
@@ -1287,14 +1287,21 @@ TEST_CASE("particle_patches", "[serial]")
     }
 }
 
-inline void dtype_test(const std::string &backend)
+inline void dtype_test(
+    const std::string &backend,
+    std::optional<std::string> activateTemplateMode = {})
 {
     bool test_long_double =
         (backend != "json" || sizeof(long double) <= 8) && backend != "toml";
     bool test_long_long =
         (backend != "json" || sizeof(long long) <= 8) && backend != "toml";
     {
-        Series s = Series("../samples/dtype_test." + backend, Access::CREATE);
+        Series s = activateTemplateMode.has_value()
+            ? Series(
+                  "../samples/dtype_test." + backend,
+                  Access::CREATE,
+                  activateTemplateMode.value())
+            : Series("../samples/dtype_test." + backend, Access::CREATE);
         bool adios1 = s.backend() == "ADIOS1" || s.backend() == "MPI_ADIOS1";
 
         char c = 'c';
@@ -1424,7 +1431,12 @@ inline void dtype_test(const std::string &backend)
         }
     }
 
-    Series s = Series("../samples/dtype_test." + backend, Access::READ_ONLY);
+    Series s = activateTemplateMode.has_value()
+        ? Series(
+              "../samples/dtype_test." + backend,
+              Access::READ_ONLY,
+              activateTemplateMode.value())
+        : Series("../samples/dtype_test." + backend, Access::READ_ONLY);
     bool adios1 = s.backend() == "ADIOS1" || s.backend() == "MPI_ADIOS1";
 
     REQUIRE(s.getAttribute("char").get<char>() == 'c');
@@ -1502,6 +1514,10 @@ inline void dtype_test(const std::string &backend)
     REQUIRE(s.getAttribute("bool").get<bool>() == true);
     REQUIRE(s.getAttribute("boolF").get<bool>() == false);
 
+    if (activateTemplateMode.has_value())
+    {
+        return;
+    }
     // same implementation types (not necessary aliases) detection
 #if !defined(_MSC_VER)
     REQUIRE(s.getAttribute("short").dtype == Datatype::SHORT);
diff --git a/test/python/unittest/API/APITest.py b/test/python/unittest/API/APITest.py
index 0aa71cf7a8..72b099c5ee 100644
--- a/test/python/unittest/API/APITest.py
+++ b/test/python/unittest/API/APITest.py
@@ -359,7 +359,8 @@ def attributeRoundTrip(self, file_ending):
         # c_types
         self.assertEqual(series.get_attribute("byte_c"), 30)
         self.assertEqual(series.get_attribute("ubyte_c"), 50)
-        if file_ending != "json":  # TODO: returns [100] instead of 100 in json
+        # TODO: returns [100] instead of 100 in json
+        if file_ending != "json" and file_ending != "toml":
             self.assertEqual(chr(series.get_attribute("char_c")), 'd')
         self.assertEqual(series.get_attribute("int16_c"), 2)
         self.assertEqual(series.get_attribute("int32_c"), 3)
@@ -1824,7 +1825,7 @@ def testIterator(self):
                 self.makeIteratorRoundTrip(b, backend_filesupport[b])
 
     def makeAvailableChunksRoundTrip(self, ext):
-        if ext == "h5":
+        if ext == "h5" or ext == "toml":
             return
         name = "../samples/available_chunks_python." + ext
         write = io.Series(