diff --git a/src/eeprom_arm.cpp b/src/eeprom_arm.cpp
index 556e2537a..435568d9f 100644
--- a/src/eeprom_arm.cpp
+++ b/src/eeprom_arm.cpp
@@ -937,8 +937,12 @@ const pm_char * eeBackupModel(uint8_t i_fileSrc)
   while (i>sizeof(MODELS_PATH)-1) {
     if (!len && buf[i])
       len = i+1;
-    if (len)
-      buf[i] = idx2char(buf[i]);
+    if (len) {
+      if (buf[i])
+        buf[i] = idx2char(buf[i]);
+      else
+        buf[i] = '_';
+    }
     i--;
   }
 
diff --git a/src/eeprom_avr.cpp b/src/eeprom_avr.cpp
index 34940d3ba..3e52828c3 100644
--- a/src/eeprom_avr.cpp
+++ b/src/eeprom_avr.cpp
@@ -566,8 +566,12 @@ const pm_char * eeBackupModel(uint8_t i_fileSrc)
   while (i>sizeof(MODELS_PATH)-1) {
     if (!len && buf[i])
       len = i+1;
-    if (len)
-      buf[i] = idx2char(buf[i]);
+    if (len) {
+      if (buf[i])
+	buf[i] = idx2char(buf[i]);
+      else
+        buf[i] = '_'; 	
+    }
     i--;
   }