diff --git a/project/Core/Src/tftp.c b/project/Core/Src/tftp.c
index c443c55..b19a12e 100644
--- a/project/Core/Src/tftp.c
+++ b/project/Core/Src/tftp.c
@@ -28,10 +28,11 @@ static tftp_custom_file_t virt_file[] = {{.name = "index.txt", .data = NULL, .le
 static int str_cat_str(char* dest, size_t dest_size, const char* src) {
     size_t dest_len = strlen(dest);
     size_t src_len = strlen(src);
-    if (dest_len + src_len > dest_size) {
+    if (dest_len + src_len >= dest_size) {
         return -1;
     }
     memcpy(dest + dest_len, src, src_len);
+    dest[dest_len + src_len] = '\0';
     return 0;
 }