diff --git a/circuitpython/code/cameteo.py b/circuitpython/code/cameteo.py
index 8688831..1da0128 100644
--- a/circuitpython/code/cameteo.py
+++ b/circuitpython/code/cameteo.py
@@ -124,9 +124,9 @@ class Data:
     def csv(self, header=False):
         """Serialized data values (or keys if header=True) as CSV line"""
         if header:
-            return ";".join(self.data.keys())
+            return ";".join([str(x) for x in self.data.keys()])
 
-        return ";".join(self.data.values())
+        return ";".join([str(x) for x in self.data.values()])
 
     def write_on_flash(self, current, verbose=True):
         """Save the current data as csv file on SPI flash"""