diff --git a/Cargo.toml b/Cargo.toml
index 786cbbd3..328cc909 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -32,4 +32,5 @@ default-features = false
 [features]
 default = []
 kip4 = []
+kip6 = []
 std = ["pwasm-std/std", "parity-hash/std", "uint/std", "byteorder/std"]
diff --git a/src/ext.rs b/src/ext.rs
index 4e2ce0af..abf4623e 100644
--- a/src/ext.rs
+++ b/src/ext.rs
@@ -62,6 +62,7 @@ mod external {
 
 		pub fn gaslimit(dest: *mut u8);
 
+		#[cfg(feature = "kip6")]
 		pub fn gasleft() -> i64;
 
 		pub fn sender(dest: *mut u8);
@@ -255,6 +256,7 @@ pub fn gas_limit() -> U256 {
 	unsafe { fetch_u256(|x| external::gaslimit(x) ) }
 }
 
+#[cfg(feature = "kip6")]
 /// Get amount of gas left.
 pub fn gas_left() -> u64 {
 	unsafe { external::gasleft() as u64 }