diff --git a/core/src/consensus.rs b/core/src/consensus.rs
index 0c8800f4d..21ca470f9 100644
--- a/core/src/consensus.rs
+++ b/core/src/consensus.rs
@@ -90,11 +90,20 @@ pub const MAX_BLOCK_WEIGHT: usize = 80_000;
 
 /// Reused consistently for various max lengths below.
 /// Max transaction is effectively a full block of data.
+/// Soft fork down when too high.
+/// Likely we will need to tweak these all individually, but using a single constant for now.
 const MAX_INP_OUT_KERN_LEN: usize = 300_000;
 
-/// Maximum inputs for a block (issue#261)
-/// Hundreds of inputs + 1 output might be slow to validate (issue#258)
-pub const MAX_BLOCK_INPUTS: usize = MAX_INP_OUT_KERN_LEN; // soft fork down when too_high
+/// Maximum inputs for a block.
+pub const MAX_BLOCK_INPUTS: usize = MAX_INP_OUT_KERN_LEN;
+
+/// Maximum outputs for a block (max tx + single output for coinbase).
+/// This is just a starting point - need to discuss this further.
+pub const MAX_BLOCK_OUTPUTS: usize = MAX_INP_OUT_KERN_LEN + 1;
+
+/// Maximum kernels for a block (max tx + single output for coinbase).
+/// This is just a starting point - need to discuss this further.
+pub const MAX_BLOCK_KERNELS: usize = MAX_INP_OUT_KERN_LEN + 1;
 
 /// Maximum inputs in a transaction.
 pub const MAX_TX_INPUTS: usize = MAX_INP_OUT_KERN_LEN;
@@ -105,13 +114,6 @@ pub const MAX_TX_OUTPUTS: usize = MAX_INP_OUT_KERN_LEN;
 /// Maximum kernels in a transaction.
 pub const MAX_TX_KERNELS: usize = MAX_INP_OUT_KERN_LEN;
 
-/// Whether a block exceeds the maximum acceptable weight
-pub fn exceeds_weight(input_len: usize, output_len: usize, kernel_len: usize) -> bool {
-	input_len * BLOCK_INPUT_WEIGHT
-		+ output_len * BLOCK_OUTPUT_WEIGHT
-		+ kernel_len * BLOCK_KERNEL_WEIGHT > MAX_BLOCK_WEIGHT || input_len > MAX_BLOCK_INPUTS
-}
-
 /// Fork every 250,000 blocks for first 2 years, simple number and just a
 /// little less than 6 months.
 pub const HARD_FORK_INTERVAL: u64 = 250_000;
diff --git a/core/src/core/block.rs b/core/src/core/block.rs
index 72acfcec1..a1dbf240f 100644
--- a/core/src/core/block.rs
+++ b/core/src/core/block.rs
@@ -21,7 +21,7 @@ use std::collections::HashSet;
 use std::fmt;
 use std::iter::FromIterator;
 
-use consensus::{self, exceeds_weight, reward, VerifySortOrder, REWARD};
+use consensus::{self, reward, VerifySortOrder, REWARD};
 use core::committed::{self, Committed};
 use core::hash::{Hash, HashWriter, Hashed, ZERO_HASH};
 use core::id::ShortIdentifiable;
@@ -45,7 +45,13 @@ pub enum Error {
 	InvalidTotalKernelSum,
 	/// Same as above but for the coinbase part of a block, including reward
 	CoinbaseSumMismatch,
-	/// Too many inputs, outputs or kernels in the block
+	/// Restrict number of block inputs.
+	TooManyInputs,
+	/// Restrict number of block outputs.
+	TooManyOutputs,
+	/// Retrict number of block kernels.
+	TooManyKernels,
+	/// Block weight (based on inputs|outputs|kernels) exceeded.
 	WeightExceeded,
 	/// Kernel not valid due to lock_height exceeding block header height
 	KernelLockHeight(u64),
@@ -399,6 +405,13 @@ impl Readable for Block {
 		let outputs = read_and_verify_sorted(reader, output_len)?;
 		let kernels = read_and_verify_sorted(reader, kernel_len)?;
 
+		// TODO - we do not verify the input|output|kernel counts here.
+		// I think should call block.validate() as part of a call to read()
+		// but block.validate() as it stands currently requires the previous sums etc.
+		// So there is no easy way to do this in isolation.
+		// Maybe we need two variations of validate() where one handles the validation
+		// rules that *can* be done in isolation.
+
 		Ok(Block {
 			header: header,
 			inputs: inputs,
@@ -694,7 +707,11 @@ impl Block {
 		prev_kernel_offset: &BlindingFactor,
 		prev_kernel_sum: &Commitment,
 	) -> Result<(Commitment), Error> {
+		// Verify we do not exceed the max number of inputs|outputs|kernels
+		// and that the "weight" based on these does not exceed the max permitted weight.
+		self.verify_size()?;
 		self.verify_weight()?;
+
 		self.verify_sorted()?;
 		self.verify_cut_through()?;
 		self.verify_coinbase()?;
@@ -727,8 +744,28 @@ impl Block {
 		Ok(kernel_sum)
 	}
 
+	// Verify the tx is not too big in terms of
+	// number of inputs|outputs|kernels.
+	fn verify_size(&self) -> Result<(), Error> {
+		if self.inputs.len() > consensus::MAX_BLOCK_INPUTS {
+			return Err(Error::TooManyInputs);
+		}
+		if self.outputs.len() > consensus::MAX_BLOCK_OUTPUTS {
+			return Err(Error::TooManyOutputs);
+		}
+		if self.kernels.len() > consensus::MAX_BLOCK_KERNELS {
+			return Err(Error::TooManyKernels);
+		}
+		Ok(())
+	}
+
 	fn verify_weight(&self) -> Result<(), Error> {
-		if exceeds_weight(self.inputs.len(), self.outputs.len(), self.kernels.len()) {
+		let weight =
+			self.inputs.len() * consensus::BLOCK_INPUT_WEIGHT +
+			self.outputs.len() * consensus::BLOCK_OUTPUT_WEIGHT +
+			self.kernels.len() * consensus::BLOCK_KERNEL_WEIGHT;
+
+		if weight > consensus::MAX_BLOCK_WEIGHT {
 			return Err(Error::WeightExceeded);
 		}
 		Ok(())