diff --git a/src/runtime/Cargo.toml b/src/runtime/Cargo.toml
index e32ef421..e6c662b4 100644
--- a/src/runtime/Cargo.toml
+++ b/src/runtime/Cargo.toml
@@ -14,7 +14,7 @@ num-traits = { version = "0.2", default-features = false }
 num-derive = "0.3"
 cslice = "0.3"
 log = "0.4"
-core_io = { version = "0.1", features = ["alloc", "collections"] }
+core_io = { version = "0.1", features = ["collections"] }
 byteorder = { version = "1.3", default-features = false }
 void = { version = "1", default-features = false }
 futures = { version = "0.3", default-features = false, features = ["async-await"] }
@@ -24,4 +24,4 @@ libsupport_zynq = { git = "https://git.m-labs.hk/M-Labs/zc706.git" }
 libcortex_a9 = { git = "https://git.m-labs.hk/M-Labs/zc706.git" }
 libasync = { git = "https://git.m-labs.hk/M-Labs/zc706.git" }
 dyld = { path = "../libdyld" }
-fatfs = { version = "0.3", features = ["core_io", "alloc"], default-features = false }
+fatfs = { version = "0.3", features = ["core_io"], default-features = false }
diff --git a/src/runtime/src/sd_reader.rs b/src/runtime/src/sd_reader.rs
index add00a13..ace2fffc 100644
--- a/src/runtime/src/sd_reader.rs
+++ b/src/runtime/src/sd_reader.rs
@@ -2,6 +2,7 @@ use core_io::{BufRead, Error, ErrorKind, Read, Result as IoResult, Seek, SeekFro
 use fatfs;
 use libboard_zynq::sdio::{sd_card::SdCard, CmdTransferError};
 use log::debug;
+use alloc::vec::Vec;
 
 fn cmd_error_to_io_error(_: CmdTransferError) -> Error {
     Error::new(ErrorKind::Other, "Command transfer error")
@@ -19,7 +20,7 @@ pub struct SdReader {
     /// Internal SdCard handle.
     sd: SdCard,
     /// Read buffer with the size of 1 block.
-    buffer: [u8; BLOCK_SIZE],
+    buffer: Vec<u8>,
     /// Address for the next byte.
     byte_addr: u32,
     /// Internal index for the next byte.
@@ -47,9 +48,13 @@ pub enum PartitionEntry {
 impl SdReader {
     /// Create SdReader from SdCard
     pub fn new(sd: SdCard) -> SdReader {
+        let mut vec: Vec<u8> = Vec::with_capacity(BLOCK_SIZE);
+        unsafe {
+            vec.set_len(vec.capacity());
+        }
         SdReader {
             sd,
-            buffer: [0; BLOCK_SIZE],
+            buffer: vec,
             byte_addr: 0,
             index: BLOCK_SIZE,
             dirty: false,