diff --git a/ethcore/engines/ethash/src/lib.rs b/ethcore/engines/ethash/src/lib.rs
index bd901ef88..acac922fd 100644
--- a/ethcore/engines/ethash/src/lib.rs
+++ b/ethcore/engines/ethash/src/lib.rs
@@ -464,7 +464,16 @@ impl Ethash {
 	}
 }
 
-fn ecip1017_eras_block_reward(era_rounds: u64, mut reward: U256, block_number:u64) -> (u64, U256) {
+
+/// Calculates the number of eras and reward
+///
+/// # Panics
+///
+/// This function will panic if `era_rounds` is less than `2`
+fn ecip1017_eras_block_reward(era_rounds: u64, mut reward: U256, block_number: u64) -> (u64, U256) {
+	// NOTE(niklasad1): all numbers is divisible by 1, it will cause the if below
+	// to succeed except for the first block. Thus, `era_rounds - 1 == 0` and cause `divide by zero`
+	assert!(era_rounds > 1, "ecip1017EraRounds must be bigger than 1");
 	let eras = if block_number != 0 && block_number % era_rounds == 0 {
 		block_number / era_rounds - 1
 	} else {
diff --git a/json/src/spec/ethash.rs b/json/src/spec/ethash.rs
index eee44d02b..2db689275 100644
--- a/json/src/spec/ethash.rs
+++ b/json/src/spec/ethash.rs
@@ -91,6 +91,7 @@ pub struct EthashParams {
 	pub ecip1010_continue_transition: Option<Uint>,
 
 	/// See main EthashParams docs.
+	#[serde(default, deserialize_with="uint::validate_optional_non_zero")]
 	pub ecip1017_era_rounds: Option<Uint>,
 
 	/// Delays of difficulty bombs.
@@ -101,7 +102,6 @@ pub struct EthashParams {
 	/// EXPIP-2 duration limit
 	pub expip2_duration_limit: Option<Uint>,
 	/// Block to transition to progpow
-	#[serde(rename="progpowTransition")]
 	pub progpow_transition: Option<Uint>,
 }