diff --git a/polkadot/runtime/wasm/Cargo.lock b/polkadot/runtime/wasm/Cargo.lock
index 74829d6520abe..82cbbb68e9895 100644
--- a/polkadot/runtime/wasm/Cargo.lock
+++ b/polkadot/runtime/wasm/Cargo.lock
@@ -137,11 +137,6 @@ dependencies = [
 name = "environmental"
 version = "0.1.0"
 
-[[package]]
-name = "error-chain"
-version = "0.11.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-
 [[package]]
 name = "ethbloom"
 version = "0.5.0"
@@ -294,16 +289,6 @@ dependencies = [
  "tiny-keccak 1.4.2 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
-[[package]]
-name = "kvdb"
-version = "0.1.0"
-source = "git+https://github.com/paritytech/parity.git#dec390a89fe038337399315daf15e628ffbb4d8e"
-dependencies = [
- "elastic-array 0.10.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "error-chain 0.11.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "ethcore-bytes 0.1.0 (git+https://github.com/paritytech/parity.git)",
-]
-
 [[package]]
 name = "lazy_static"
 version = "0.2.11"
@@ -995,7 +980,6 @@ dependencies = [
  "ethereum-types 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "hashdb 0.1.1 (git+https://github.com/paritytech/parity.git)",
  "hex-literal 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "kvdb 0.1.0 (git+https://github.com/paritytech/parity.git)",
  "log 0.3.9 (registry+https://github.com/rust-lang/crates.io-index)",
  "memorydb 0.1.1 (git+https://github.com/paritytech/parity.git)",
  "parking_lot 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1182,7 +1166,6 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum crunchy 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)" = "a2f4a431c5c9f662e1200b7c7f02c34e91361150e382089a8f2dec3ba680cbda"
 "checksum elastic-array 0.10.0 (registry+https://github.com/rust-lang/crates.io-index)" = "88d4851b005ef16de812ea9acdb7bece2f0a40dd86c07b85631d7dafa54537bb"
 "checksum env_logger 0.4.3 (registry+https://github.com/rust-lang/crates.io-index)" = "3ddf21e73e016298f5cb37d6ef8e8da8e39f91f9ec8b0df44b7deb16a9f8cd5b"
-"checksum error-chain 0.11.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ff511d5dc435d703f4971bc399647c9bc38e20cb41452e3b9feb4765419ed3f3"
 "checksum ethbloom 0.5.0 (registry+https://github.com/rust-lang/crates.io-index)" = "1a93a43ce2e9f09071449da36bfa7a1b20b950ee344b6904ff23de493b03b386"
 "checksum ethcore-bytes 0.1.0 (git+https://github.com/paritytech/parity.git)" = "<none>"
 "checksum ethcore-logger 1.12.0 (git+https://github.com/paritytech/parity.git)" = "<none>"
@@ -1200,7 +1183,6 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum integer-sqrt 0.1.0 (git+https://github.com/paritytech/integer-sqrt-rs.git)" = "<none>"
 "checksum keccak-hash 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "0b7f51f30d7986536accaec4a6a288008dfb3dbffe8a2863a65292bc395a3ae7"
 "checksum keccak-hash 0.1.2 (git+https://github.com/paritytech/parity.git)" = "<none>"
-"checksum kvdb 0.1.0 (git+https://github.com/paritytech/parity.git)" = "<none>"
 "checksum lazy_static 0.2.11 (registry+https://github.com/rust-lang/crates.io-index)" = "76f033c7ad61445c5b347c7382dd1237847eb1bce590fe50365dcb33d546be73"
 "checksum lazy_static 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)" = "e6412c5e2ad9584b0b8e979393122026cdd6d2a80b933f890dcd694ddbe73739"
 "checksum libc 0.2.41 (registry+https://github.com/rust-lang/crates.io-index)" = "ac8ebf8343a981e2fa97042b14768f02ed3e1d602eac06cae6166df3c8ced206"
diff --git a/substrate/runtime/staking/src/lib.rs b/substrate/runtime/staking/src/lib.rs
index 3237584b84aeb..c3c1800d4b47b 100644
--- a/substrate/runtime/staking/src/lib.rs
+++ b/substrate/runtime/staking/src/lib.rs
@@ -557,8 +557,8 @@ impl<T: Trait> Module<T> {
 		if normal_rotation {
 			// reward
 			let ideal_elapsed = <session::Module<T>>::ideal_session_duration();
-			let percent: usize = (T::Moment::sa(65536usize) * ideal_elapsed.clone() / actual_elapsed.max(ideal_elapsed)).as_();
-			let reward = Self::session_reward() * T::Balance::sa(percent) / T::Balance::sa(65536usize);
+			let per65536: u64 = (T::Moment::sa(65536u64) * ideal_elapsed.clone() / actual_elapsed.max(ideal_elapsed)).as_();
+			let reward = Self::session_reward() * T::Balance::sa(per65536) / T::Balance::sa(65536u64);
 			// apply good session reward
 			for v in <session::Module<T>>::validators().iter() {
 				let noms = Self::current_nominators_for(v);
@@ -577,12 +577,12 @@ impl<T: Trait> Module<T> {
 			for v in <session::Module<T>>::validators().iter() {
 				if let Some(rem) = Self::slash(v, early_era_slash) {
 					let noms = Self::current_nominators_for(v);
-					let total = noms.iter().map(Self::voting_balance).fold(Zero::zero(), |acc, x| acc + x);
-					for n in noms.iter() {
-						//let r = Self::voting_balance(n) * reward / total;	// correct formula, but might overflow with large slash * total.
-						let quant = T::Balance::sa(1usize << 31);
-						let s = (Self::voting_balance(n) * quant / total) * rem / quant; // avoid overflow by using quant as a denominator.
-						let _ = Self::slash(n, s);	// best effort - not much that can be done on fail.
+					let total = noms.iter().map(Self::voting_balance).fold(T::Balance::zero(), |acc, x| acc + x);
+					if !total.is_zero() {
+						let safe_mul_rational = |b| b * rem / total;// TODO: avoid overflow
+						for n in noms.iter() {
+							let _ = Self::slash(n, safe_mul_rational(Self::voting_balance(n)));	// best effort - not much that can be done on fail.
+						}
 					}
 				}
 			}