diff --git a/src/extrinsic/mod.rs b/src/extrinsic/mod.rs
index c3b90feac0..65643db1e0 100644
--- a/src/extrinsic/mod.rs
+++ b/src/extrinsic/mod.rs
@@ -17,7 +17,6 @@
 //! Create signed or unsigned extrinsics.
 
 mod extra;
-mod mortal_period;
 mod signer;
 
 pub use self::{
@@ -26,7 +25,6 @@ pub use self::{
         Extra,
         SignedExtra,
     },
-    mortal_period::derive_mortal_period,
     signer::{
         PairSigner,
         Signer,
diff --git a/src/extrinsic/mortal_period.rs b/src/extrinsic/mortal_period.rs
deleted file mode 100644
index 115705438a..0000000000
--- a/src/extrinsic/mortal_period.rs
+++ /dev/null
@@ -1,55 +0,0 @@
-// Copyright 2019-2020 Parity Technologies (UK) Ltd.
-// This file is part of substrate-subxt.
-//
-// subxt is free software: you can redistribute it and/or modify
-// it under the terms of the GNU General Public License as published by
-// the Free Software Foundation, either version 3 of the License, or
-// (at your option) any later version.
-//
-// subxt is distributed in the hope that it will be useful,
-// but WITHOUT ANY WARRANTY; without even the implied warranty of
-// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-// GNU General Public License for more details.
-//
-// You should have received a copy of the GNU General Public License
-// along with substrate-subxt.  If not, see <http://www.gnu.org/licenses/>.
-
-use crate::{
-    Error,
-    Metadata,
-};
-
-/// 5 min `mortal_period` in milliseconds, to be adjusted based on expected block time
-pub const BASELINE_MORTAL_PERIOD: u64 = 5 * 60 * 1000;
-
-/// Fallback `BlockHashCount` of 2,400 blocks
-pub const FALLBACK_BLOCK_HASH_COUNT: u64 = 2_400;
-
-/// Fallback expected block time of 6,000 milliseconds
-pub const FALLBACK_EXPECTED_BLOCK_TIME: u64 = 6_000;
-
-/// Derive a default mortal period based on a chain's metadata
-pub fn derive_mortal_period(metadata: &Metadata) -> Result<u64, Error> {
-    let block_hash_count = if let Ok(system_meta) = metadata.module("System") {
-        if let Ok(count) = system_meta.constant("BlockHashCount") {
-            count.value::<u32>()?.into()
-        } else {
-            FALLBACK_BLOCK_HASH_COUNT
-        }
-    } else {
-        FALLBACK_BLOCK_HASH_COUNT
-    };
-    let block_time = if let Ok(babe_meta) = metadata.module("Babe") {
-        if let Ok(milliseconds) = babe_meta.constant("ExpectedBlockTime") {
-            milliseconds.value::<u64>()?
-        } else {
-            FALLBACK_EXPECTED_BLOCK_TIME
-        }
-    } else {
-        FALLBACK_EXPECTED_BLOCK_TIME
-    };
-
-    Ok((BASELINE_MORTAL_PERIOD / block_time)
-        .next_power_of_two()
-        .min(block_hash_count.next_power_of_two()))
-}
diff --git a/src/lib.rs b/src/lib.rs
index b69fead1ff..f542bb188d 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -89,7 +89,6 @@ pub use crate::{
         RawEvent,
     },
     extrinsic::{
-        derive_mortal_period,
         PairSigner,
         SignedExtra,
         Signer,
@@ -180,8 +179,8 @@ impl<T: Runtime> ClientBuilder<T> {
             rpc.system_properties(),
         )
         .await;
-        let metadata = metadata?;
-        let mortal_period = derive_mortal_period(&metadata).ok();
+		let metadata = metadata?;
+		let mortal_period = Some(metadata.derive_mortal_period()?);
         Ok(Client {
             rpc,
             genesis_hash: genesis_hash?,
diff --git a/src/metadata.rs b/src/metadata.rs
index 27b3446cbd..3b9769b81f 100644
--- a/src/metadata.rs
+++ b/src/metadata.rs
@@ -40,6 +40,15 @@ use sp_core::storage::StorageKey;
 
 use crate::Encoded;
 
+/// 5 min `mortal_period`in milliseconds, to be adjusted based on expected block time
+pub const BASELINE_MORTAL_PERIOD: u64 = 5 * 60 * 1000;
+
+/// Fallback `BlockHashCount`
+pub const FALLBACK_BLOCK_HASH_COUNT: u64 = 2_400;
+
+/// Fallback expected block time in milliseconds
+pub const FALLBACK_EXPECTED_BLOCK_TIME: u64 = 6_000;
+
 /// Metadata error.
 #[derive(Debug, thiserror::Error)]
 pub enum MetadataError {
@@ -164,7 +173,33 @@ impl Metadata {
             }
         }
         string
-    }
+	}
+
+	/// Derive a default mortal period
+	pub(crate) fn derive_mortal_period(&self) -> Result<u64, MetadataError> {
+		let block_hash_count = if let Ok(system_meta) = self.module("System") {
+			if let Ok(count) = system_meta.constant("BlockHashCount") {
+				count.value::<u32>()?.into()
+			} else {
+				FALLBACK_BLOCK_HASH_COUNT
+			}
+		} else {
+			FALLBACK_BLOCK_HASH_COUNT
+		};
+		let block_time = if let Ok(babe_meta) = self.module("Babe") {
+			if let Ok(milliseconds) = babe_meta.constant("ExpectedBlockTime") {
+				milliseconds.value::<u64>()?
+			} else {
+				FALLBACK_EXPECTED_BLOCK_TIME
+			}
+		} else {
+			FALLBACK_EXPECTED_BLOCK_TIME
+		};
+
+		Ok((BASELINE_MORTAL_PERIOD / block_time)
+			.next_power_of_two()
+			.min(block_hash_count.next_power_of_two()))
+	}
 }
 
 #[derive(Clone, Debug)]