diff --git a/ampel-firmware/csv_writer.cpp b/ampel-firmware/csv_writer.cpp
index 4dd09360eb30c9f6a74d4a7b607e57c80d96e659..68f064a795e38baee23720db3c2a072837e5610c 100644
--- a/ampel-firmware/csv_writer.cpp
+++ b/ampel-firmware/csv_writer.cpp
@@ -121,7 +121,7 @@ namespace csv_writer {
     Serial.println();
 
     // Open dir folder
-    Serial.println("Filesystem content:");
+    Serial.println(F("Filesystem content:"));
     showFilesystemContent();
     Serial.println();