diff --git a/pythonfmu/default_experiment.py b/pythonfmu/default_experiment.py
index 817cf08..1bb70d5 100644
--- a/pythonfmu/default_experiment.py
+++ b/pythonfmu/default_experiment.py
@@ -1,6 +1,6 @@
 class DefaultExperiment:
 
-    def __init__(self, start_time: float = None, stop_time: float = None, tolerance: float = None):
-        self.start_time = start_time
-        self.stop_time = stop_time
-        self.tolerance = tolerance
+    def __init__(self, start_time = None, stop_time = None, tolerance = None):
+        self.start_time = str(start_time) if start_time is not None else None
+        self.stop_time = str(stop_time) if stop_time is not None else None
+        self.tolerance = str(tolerance) if tolerance is not None else None
diff --git a/pythonfmu/fmi2slave.py b/pythonfmu/fmi2slave.py
index 8780829..d2ea4b3 100644
--- a/pythonfmu/fmi2slave.py
+++ b/pythonfmu/fmi2slave.py
@@ -129,13 +129,18 @@ class Fmi2Slave(ABC):
 
         if self.default_experiment is not None:
             attrib = dict()
+            has_attrib = False
             if self.default_experiment.start_time is not None:
                 attrib["startTime"] = self.default_experiment.start_time
+                has_attrib = True
             if self.default_experiment.stop_time is not None:
                 attrib["stopTime"] = self.default_experiment.stop_time
+                has_attrib = True
             if self.default_experiment.tolerance is not None:
                 attrib["tolerance"] = self.default_experiment.tolerance
-            SubElement(root, "DefaultExperiment", attrib)
+                has_attrib = True
+            if has_attrib:
+                SubElement(root, "DefaultExperiment", attrib)
 
         return root