diff --git a/Marlin/SdBaseFile.cpp b/Marlin/SdBaseFile.cpp
index dbcf77fbdc..c72eced73c 100644
--- a/Marlin/SdBaseFile.cpp
+++ b/Marlin/SdBaseFile.cpp
@@ -1012,7 +1012,7 @@ void SdBaseFile::printFatTime( uint16_t fatTime) {
  * the value zero, false, is returned for failure.
  */
 bool SdBaseFile::printName() {
-  char name[13];
+  char name[FILENAME_LENGTH];
   if (!getFilename(name)) return false;
   MYSERIAL.print(name);
   return true;
@@ -1135,7 +1135,7 @@ int8_t SdBaseFile::readDir(dir_t* dir, char* longFilename) {
     	if (VFAT->firstClusterLow == 0 && (VFAT->sequenceNumber & 0x1F) > 0 && (VFAT->sequenceNumber & 0x1F) <= MAX_VFAT_ENTRIES)
     	{
 			//TODO: Store the filename checksum to verify if a none-long filename aware system modified the file table.
-    		n = ((VFAT->sequenceNumber & 0x1F) - 1) * 13;
+    		n = ((VFAT->sequenceNumber & 0x1F) - 1) * FILENAME_LENGTH;
 			longFilename[n+0] = VFAT->name1[0];
 			longFilename[n+1] = VFAT->name1[1];
 			longFilename[n+2] = VFAT->name1[2];
@@ -1151,7 +1151,7 @@ int8_t SdBaseFile::readDir(dir_t* dir, char* longFilename) {
 			longFilename[n+12] = VFAT->name3[1];
 			//If this VFAT entry is the last one, add a NUL terminator at the end of the string
 			if (VFAT->sequenceNumber & 0x40)
-				longFilename[n+13] = '\0';
+				longFilename[n+FILENAME_LENGTH] = '\0';
 		}
     }
     // return if normal file or subdirectory
diff --git a/Marlin/SdFatConfig.h b/Marlin/SdFatConfig.h
index 24caf6f3eb..a549835f70 100644
--- a/Marlin/SdFatConfig.h
+++ b/Marlin/SdFatConfig.h
@@ -108,15 +108,17 @@ uint8_t const SOFT_SPI_SCK_PIN = 13;
  * a pure virtual function is called.
  */
 #define USE_CXA_PURE_VIRTUAL 1
+
+/** Number of UTF-16 characters per entry */
+#define FILENAME_LENGTH 13
+
 /**
  * Defines for long (vfat) filenames
  */
 /** Number of VFAT entries used. Every entry has 13 UTF-16 characters */
 #define MAX_VFAT_ENTRIES (2)
-/** Number of UTF-16 characters per entry */
-#define FILENAME_LENGTH 13
 /** Total size of the buffer used to store the long filenames */
-#define LONG_FILENAME_LENGTH (13*MAX_VFAT_ENTRIES+1)
+#define LONG_FILENAME_LENGTH (FILENAME_LENGTH*MAX_VFAT_ENTRIES+1)
 #endif  // SdFatConfig_h
 
 
diff --git a/Marlin/cardreader.cpp b/Marlin/cardreader.cpp
index e22f3436b6..83671e00d0 100644
--- a/Marlin/cardreader.cpp
+++ b/Marlin/cardreader.cpp
@@ -23,7 +23,7 @@ CardReader::CardReader()
    memset(workDirParents, 0, sizeof(workDirParents));
 
    autostart_stilltocheck=true; //the SD start is delayed, because otherwise the serial cannot answer fast enough to make contact with the host software.
-   lastnr=0;
+   autostart_index=0;
   //power to SD reader
   #if SDPOWER > -1
     SET_OUTPUT(SDPOWER); 
@@ -60,8 +60,8 @@ void CardReader::lsDive(const char *prepend, SdFile parent, const char * const m
     if( DIR_IS_SUBDIR(&p) && lsAction!=LS_Count && lsAction!=LS_GetFilename) // hence LS_SerialPrint
     {
 
-      char path[13*2];
-      char lfilename[13];
+      char path[FILENAME_LENGTH*2];
+      char lfilename[FILENAME_LENGTH];
       createFilename(lfilename,p);
       
       path[0]=0;
@@ -241,7 +241,7 @@ void CardReader::getAbsFilename(char *t)
     while(*t!=0 && cnt< MAXPATHNAMELENGTH) 
     {t++;cnt++;}  //crawl counter forward.
   }
-  if(cnt<MAXPATHNAMELENGTH-13)
+  if(cnt<MAXPATHNAMELENGTH-FILENAME_LENGTH)
     file.getFilename(t);
   else
     t[0]=0;
@@ -311,7 +311,7 @@ void CardReader::openFile(char* name,bool read, bool replace_current/*=true*/)
       //SERIAL_ECHO("end  :");SERIAL_ECHOLN((int)(dirname_end-name));
       if(dirname_end>0 && dirname_end>dirname_start)
       {
-        char subdirname[13];
+        char subdirname[FILENAME_LENGTH];
         strncpy(subdirname, dirname_start, dirname_end-dirname_start);
         subdirname[dirname_end-dirname_start]=0;
         SERIAL_ECHOLN(subdirname);
@@ -408,7 +408,7 @@ void CardReader::removeFile(char* name)
       //SERIAL_ECHO("end  :");SERIAL_ECHOLN((int)(dirname_end-name));
       if(dirname_end>0 && dirname_end>dirname_start)
       {
-        char subdirname[13];
+        char subdirname[FILENAME_LENGTH];
         strncpy(subdirname, dirname_start, dirname_end-dirname_start);
         subdirname[dirname_end-dirname_start]=0;
         SERIAL_ECHOLN(subdirname);
@@ -510,7 +510,7 @@ void CardReader::checkautostart(bool force)
   }
   
   char autoname[30];
-  sprintf_P(autoname, PSTR("auto%i.g"), lastnr);
+  sprintf_P(autoname, PSTR("auto%i.g"), autostart_index);
   for(int8_t i=0;i<(int8_t)strlen(autoname);i++)
     autoname[i]=tolower(autoname[i]);
   dir_t p;
@@ -537,9 +537,9 @@ void CardReader::checkautostart(bool force)
     }
   }
   if(!found)
-    lastnr=-1;
+    autostart_index=-1;
   else
-    lastnr++;
+    autostart_index++;
 }
 
 void CardReader::closefile(bool store_location)
diff --git a/Marlin/cardreader.h b/Marlin/cardreader.h
index e513dc064f..a1da3d64a3 100644
--- a/Marlin/cardreader.h
+++ b/Marlin/cardreader.h
@@ -50,12 +50,12 @@ public:
 public:
   bool saving;
   bool logging;
-  bool sdprinting ;  
-  bool cardOK ;
-  char filename[13];
+  bool sdprinting;  
+  bool cardOK;
+  char filename[FILENAME_LENGTH];
   char longFilename[LONG_FILENAME_LENGTH];
   bool filenameIsDir;
-  int lastnr; //last number of the autostart;
+  int autostart_index;
 private:
   SdFile root,*curDir,workDir,workDirParents[MAX_DIR_DEPTH];
   uint16_t workDirDepth;
@@ -63,7 +63,7 @@ private:
   SdVolume volume;
   SdFile file;
   #define SD_PROCEDURE_DEPTH 1
-  #define MAXPATHNAMELENGTH (13*MAX_DIR_DEPTH+MAX_DIR_DEPTH+1)
+  #define MAXPATHNAMELENGTH (FILENAME_LENGTH*MAX_DIR_DEPTH+MAX_DIR_DEPTH+1)
   uint8_t file_subcall_ctr;
   uint32_t filespos[SD_PROCEDURE_DEPTH];
   char filenames[SD_PROCEDURE_DEPTH][MAXPATHNAMELENGTH];
diff --git a/Marlin/ultralcd.cpp b/Marlin/ultralcd.cpp
index 0f7645c873..a1ee315155 100644
--- a/Marlin/ultralcd.cpp
+++ b/Marlin/ultralcd.cpp
@@ -377,7 +377,7 @@ static void lcd_main_menu()
 #ifdef SDSUPPORT
 static void lcd_autostart_sd()
 {
-    card.lastnr=0;
+    card.autostart_index=0;
     card.setroot();
     card.checkautostart(true);
 }