diff --git a/substrate/client/basic-authorship/src/basic_authorship.rs b/substrate/client/basic-authorship/src/basic_authorship.rs
index 89edfac0d4..2fe7ba72ec 100644
--- a/substrate/client/basic-authorship/src/basic_authorship.rs
+++ b/substrate/client/basic-authorship/src/basic_authorship.rs
@@ -42,6 +42,15 @@ use std::marker::PhantomData;
 use prometheus_endpoint::Registry as PrometheusRegistry;
 use sc_proposer_metrics::MetricsLink as PrometheusMetrics;
 
+/// Default maximum block size in bytes used by [`Proposer`].
+///
+/// Can be overwritten by [`ProposerFactory::set_maxium_block_size`].
+///
+/// Be aware that there is also an upper packet size on what the networking code
+/// will accept. If the block doesn't fit in such a package, it can not be
+/// transferred to other nodes.
+pub const DEFAULT_MAX_BLOCK_SIZE: usize = 4 * 1024 * 1024 + 512;
+
 /// Proposer factory.
 pub struct ProposerFactory<A, B, C> {
 	spawn_handle: Box<dyn SpawnNamed>,
@@ -53,6 +62,7 @@ pub struct ProposerFactory<A, B, C> {
 	metrics: PrometheusMetrics,
 	/// phantom member to pin the `Backend` type.
 	_phantom: PhantomData<B>,
+	max_block_size: usize,
 }
 
 impl<A, B, C> ProposerFactory<A, B, C> {
@@ -68,8 +78,17 @@ impl<A, B, C> ProposerFactory<A, B, C> {
 			transaction_pool,
 			metrics: PrometheusMetrics::new(prometheus),
 			_phantom: PhantomData,
+			max_block_size: DEFAULT_MAX_BLOCK_SIZE,
 		}
 	}
+
+	/// Set the maximum block size in bytes.
+	///
+	/// The default value for the maximum block size is:
+	/// [`DEFAULT_MAX_BLOCK_SIZE`].
+	pub fn set_maximum_block_size(&mut self, size: usize) {
+		self.max_block_size = size;
+	}
 }
 
 impl<B, Block, C, A> ProposerFactory<A, B, C>
@@ -103,6 +122,7 @@ impl<B, Block, C, A> ProposerFactory<A, B, C>
 			now,
 			metrics: self.metrics.clone(),
 			_phantom: PhantomData,
+			max_block_size: self.max_block_size,
 		};
 
 		proposer
@@ -143,6 +163,7 @@ pub struct Proposer<B, Block: BlockT, C, A: TransactionPool> {
 	now: Box<dyn Fn() -> time::Instant + Send + Sync>,
 	metrics: PrometheusMetrics,
 	_phantom: PhantomData<B>,
+	max_block_size: usize,
 }
 
 impl<A, B, Block, C> sp_consensus::Proposer<Block> for
@@ -334,7 +355,12 @@ impl<A, B, Block, C> Proposer<B, Block, C, A>
 			error!("Failed to verify block encoding/decoding");
 		}
 
-		if let Err(err) = evaluation::evaluate_initial(&block, &self.parent_hash, self.parent_number) {
+		if let Err(err) = evaluation::evaluate_initial(
+			&block,
+			&self.parent_hash,
+			self.parent_number,
+			self.max_block_size,
+		) {
 			error!("Failed to evaluate authored block: {:?}", err);
 		}
 
diff --git a/substrate/primitives/consensus/common/src/evaluation.rs b/substrate/primitives/consensus/common/src/evaluation.rs
index edb148cdaa..fc9ab24d15 100644
--- a/substrate/primitives/consensus/common/src/evaluation.rs
+++ b/substrate/primitives/consensus/common/src/evaluation.rs
@@ -17,8 +17,6 @@
 
 //! Block evaluation and evaluation errors.
 
-use super::MAX_BLOCK_SIZE;
-
 use codec::Encode;
 use sp_runtime::traits::{Block as BlockT, Header as HeaderT, One, CheckedConversion};
 
@@ -42,11 +40,8 @@ pub enum Error {
 	#[error("Proposal had wrong number. Expected {expected:?}, got {got:?}")]
 	WrongNumber { expected: BlockNumber, got: BlockNumber },
 	/// Proposal exceeded the maximum size.
-	#[error(
-		"Proposal exceeded the maximum size of {} by {} bytes.",
-		MAX_BLOCK_SIZE, .0.saturating_sub(MAX_BLOCK_SIZE)
-	)]
-	ProposalTooLarge(usize),
+	#[error("Proposal size {block_size} exceeds maximum allowed size of {max_block_size}.")]
+	ProposalTooLarge { block_size: usize, max_block_size: usize },
 }
 
 /// Attempt to evaluate a substrate block as a node block, returning error
@@ -55,28 +50,29 @@ pub fn evaluate_initial<Block: BlockT>(
 	proposal: &Block,
 	parent_hash: &<Block as BlockT>::Hash,
 	parent_number: <<Block as BlockT>::Header as HeaderT>::Number,
+	max_block_size: usize,
 ) -> Result<()> {
 
 	let encoded = Encode::encode(proposal);
 	let proposal = Block::decode(&mut &encoded[..])
 		.map_err(|e| Error::BadProposalFormat(e))?;
 
-	if encoded.len() > MAX_BLOCK_SIZE {
-		return Err(Error::ProposalTooLarge(encoded.len()))
+	if encoded.len() > max_block_size {
+		return Err(Error::ProposalTooLarge { max_block_size, block_size: encoded.len() })
 	}
 
 	if *parent_hash != *proposal.header().parent_hash() {
 		return Err(Error::WrongParentHash {
 			expected: format!("{:?}", *parent_hash),
 			got: format!("{:?}", proposal.header().parent_hash())
-		});
+		})
 	}
 
 	if parent_number + One::one() != *proposal.header().number() {
 		return Err(Error::WrongNumber {
 			expected: parent_number.checked_into::<u128>().map(|x| x + 1),
 			got: (*proposal.header().number()).checked_into::<u128>(),
-		});
+		})
 	}
 
 	Ok(())
diff --git a/substrate/primitives/consensus/common/src/lib.rs b/substrate/primitives/consensus/common/src/lib.rs
index 47de067411..988aa7a816 100644
--- a/substrate/primitives/consensus/common/src/lib.rs
+++ b/substrate/primitives/consensus/common/src/lib.rs
@@ -46,9 +46,6 @@ pub mod import_queue;
 pub mod evaluation;
 mod metrics;
 
-// block size limit.
-const MAX_BLOCK_SIZE: usize = 4 * 1024 * 1024 + 512;
-
 pub use self::error::Error;
 pub use block_import::{
 	BlockImport, BlockOrigin, ForkChoiceStrategy, ImportedAux, BlockImportParams, BlockCheckParams,