diff --git a/src/precompiles/blake2.rs b/src/precompiles/blake2.rs
index 3541fe82b..bf5e7acb9 100644
--- a/src/precompiles/blake2.rs
+++ b/src/precompiles/blake2.rs
@@ -204,7 +204,8 @@ mod tests {
             0300000000000000\
             0000000000000000\
             00",
-        ).unwrap();
+        )
+        .unwrap();
         blake2f(&input, Some(12)).unwrap().1
     }
 
@@ -259,7 +260,9 @@ mod tests {
 
         let expected = hex::decode(
             "75ab69d3190a562c51aef8d88f1c2775876944407270c42c9844252c26d28752\
-            98743e7f6d5ea2f2d3e8d226039cd31b4e426ac4f2d3d666a610c2116fde4735").unwrap();
+            98743e7f6d5ea2f2d3e8d226039cd31b4e426ac4f2d3d666a610c2116fde4735",
+        )
+        .unwrap();
         assert_eq!(test_blake2f_final_block_false(), expected);
     }
 }
diff --git a/src/precompiles/bn128.rs b/src/precompiles/bn128.rs
index 6beb68f5e..7c6ed07a7 100644
--- a/src/precompiles/bn128.rs
+++ b/src/precompiles/bn128.rs
@@ -1,7 +1,7 @@
+use crate::precompiles::util::check_gas;
 use crate::precompiles::PrecompileResult;
 use crate::prelude::*;
 use evm::{ExitError, ExitSucceed};
-use crate::precompiles::util::check_gas;
 
 /// bn128 costs.
 mod costs {
@@ -105,7 +105,10 @@ pub(crate) fn alt_bn128_mul(input: &[u8], target_gas: Option<u64>) -> Precompile
 pub(crate) fn alt_bn128_pair(input: &[u8], target_gas: Option<u64>) -> PrecompileResult {
     use bn::{arith::U256, AffineG1, AffineG2, Fq, Fq2, Group, Gt, G1, G2};
 
-    check_gas(target_gas, costs::PAIR_PER_POINT * input.len() as u64 / 192u64 + costs::PAIR)?;
+    check_gas(
+        target_gas,
+        costs::PAIR_PER_POINT * input.len() as u64 / 192u64 + costs::PAIR,
+    )?;
 
     if input.len() % 192 != 0 {
         return Err(ExitError::Other(Borrowed(
diff --git a/src/precompiles/mod.rs b/src/precompiles/mod.rs
index e3369ab0e..57703e013 100644
--- a/src/precompiles/mod.rs
+++ b/src/precompiles/mod.rs
@@ -44,7 +44,7 @@ pub fn istanbul_precompiles(
             hash::ripemd160(input).as_bytes().to_vec(),
             0,
         ))),
-        4 => Some(Ok((ExitSucceed::Returned, identity(input).to_vec(), 0))),
+        4 => Some(identity(input, target_gas)),
         5 => match modexp::modexp(input, target_gas) {
             Ok(r) => Some(Ok((ExitSucceed::Returned, r, 0))),
             Err(e) => Some(Err(e)),
@@ -58,10 +58,21 @@ pub fn istanbul_precompiles(
     }
 }
 
+mod costs {
+    pub(super) const IDENTITY_BASE: u64 = 15;
+
+    pub(super) const IDENTITY_PER_WORD: u64 = 3;
+}
+
+/// Takes the input bytes, copies them, and returns it as the output.
+///
 /// See: https://ethereum.github.io/yellowpaper/paper.pdf
 /// See: https://etherscan.io/address/0000000000000000000000000000000000000004
-fn identity(input: &[u8]) -> &[u8] {
-    input
+fn identity(input: &[u8], target_gas: Option<u64>) -> PrecompileResult {
+    let cost = (input.len() + 31) as u64 / 32 * costs::IDENTITY_PER_WORD + costs::IDENTITY_BASE;
+    util::check_gas(target_gas, cost)?;
+
+    Ok((ExitSucceed::Returned, input.to_vec(), 0))
 }
 
 #[cfg(test)]
@@ -70,6 +81,22 @@ mod tests {
 
     #[test]
     fn test_identity() {
-        assert_eq!(identity(b""), b"")
+        let input = [0u8, 1, 2, 3];
+
+        let expected = input[0..2].to_vec();
+        let res = identity(&input[0..2], Some(18)).unwrap().1;
+        assert_eq!(res, expected);
+
+        let expected = input.to_vec();
+        let res = identity(&input, Some(18)).unwrap().1;
+
+        // gas fail
+        let res = identity(&input[0..2], Some(17));
+        assert!(matches!(res, Err(ExitError::OutOfGas)));
+
+        // larger input
+        let input = [0u8, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32];
+        let res = identity(&input, Some(21)).unwrap().1;
+        assert_eq!(res, input.to_vec());
     }
 }