diff --git a/include/teensy.h b/include/teensy.h
index ab0adfa..283e721 100644
--- a/include/teensy.h
+++ b/include/teensy.h
@@ -36,11 +36,11 @@ void initFile() {
 
   int i = 1;
   Serial.print("simOut_" + String(i) + ".csv");
-  String fileName;
+  const char *fileName;
 
   if (SD.exists("simOut.csv")) {
     while (i > 0) {
-      fileName = "simOut_" + String(i) + ".csv";
+      fileName = ("simOut_" + String(i) + ".csv").c_str();
 
       if (!SD.exists(fileName)) {
         // Open simOut_i.csv