diff --git a/ampel-firmware/csv_writer.cpp b/ampel-firmware/csv_writer.cpp
index b8a5f43be1a07f3cf2b1e6a662a14f6497469cb0..622ea5a0ace2bab758727da7854530da62fedaf0 100644
--- a/ampel-firmware/csv_writer.cpp
+++ b/ampel-firmware/csv_writer.cpp
@@ -79,14 +79,14 @@ namespace csv_writer {
   }
 #endif
 
-  char filename[20]; // "/ESPxxxxxx.csv\0"
+  char filename[20]; // e.g. "/ESPxxxxxx.csv\0"
 
   int getAvailableSpace() {
     return getTotalSpace() - getUsedSpace();
   }
 
-  void initialize(const char *sensorId) {
-    snprintf(filename, sizeof(filename), "/%.15s.csv", sensorId);
+  void initialize(const char *basename) {
+    snprintf(filename, sizeof(filename), "/%.14s.csv", basename);
 
     Serial.println();
     Serial.print(F("Initializing FS..."));
diff --git a/ampel-firmware/csv_writer.h b/ampel-firmware/csv_writer.h
index 2afa4b628a956de177cea6467d526610cda9b72b..1336637ce7790402c00c8d586a7d1312345bf766 100644
--- a/ampel-firmware/csv_writer.h
+++ b/ampel-firmware/csv_writer.h
@@ -13,7 +13,7 @@
 
 namespace csv_writer {
   extern char last_successful_write[];
-  void initialize(const char *sensorId);
+  void initialize(const char *basename);
   void logIfTimeHasCome(const char *timestamp, const int16_t &co2, const float &temperature, const float &humidity);
   int getAvailableSpace();
   extern char filename[];