diff --git a/program/src/close.rs b/program/src/close.rs
index e512da3..a4400d8 100644
--- a/program/src/close.rs
+++ b/program/src/close.rs
@@ -39,7 +39,7 @@ pub fn process_close(accounts: &[AccountInfo<'_>], _data: &[u8]) -> ProgramResul
         miner_rewards_info.as_associated_token_account(&miner_info.key, &mint_info.key)?;
     }
 
-    // Payout block reward.
+    // Payout block reward to winning miner.
     if block.best_hash_miner != Pubkey::default() {
         // Load recipient.
         recipient_info.as_associated_token_account(&block.best_hash_miner, &mint_info.key)?;
diff --git a/program/src/open.rs b/program/src/open.rs
index a12c670..f59c4d4 100644
--- a/program/src/open.rs
+++ b/program/src/open.rs
@@ -12,34 +12,42 @@ pub fn process_open(accounts: &[AccountInfo<'_>], data: &[u8]) -> ProgramResult
         return Err(ProgramError::NotEnoughAccountKeys);
     };
     signer_info.is_signer()?;
-    block_info
-        .is_empty()? // Account has not been initialized
-        .is_writable()? // Account is writable
-        .has_seeds(&[BLOCK, &id.to_le_bytes()], &ore_api::ID)?; // Account has correct seeds
     market_info
         .as_account::<Market>(&ore_api::ID)?
         .assert(|m| m.block_id < id)?; // Only allow opening blocks in forward bias
     system_program.is_program(&system_program::ID)?;
     ore_program.is_program(&ore_api::ID)?;
 
-    // Create block account.
-    create_program_account::<Block>(
-        block_info,
-        system_program,
-        signer_info,
-        &ore_api::ID,
-        &[BLOCK, &id.to_le_bytes()],
-    )?;
-    let block = block_info.as_account_mut::<Block>(&ore_api::ID)?;
-    block.id = id;
-    block.opener = *signer_info.key;
-    block.best_hash = [0; 32];
-    block.best_hash_miner = Pubkey::default();
-    block.reward = 0; // Set by reset instruction
-    block.start_slot = u64::MAX; // Set by reset instruction
-    block.end_slot = u64::MAX; // Set by reset instruction
-    block.slot_hash = [0; 32]; // Set by reset instruction
-    block.total_hashpower = 0;
+    // Create block, if it doesn't exist.
+    if block_info.data_is_empty() {
+        block_info
+            .is_empty()? // Account has not been initialized
+            .is_writable()? // Account is writable
+            .has_seeds(&[BLOCK, &id.to_le_bytes()], &ore_api::ID)?; // Account has correct seeds
+
+        // Create block account.
+        create_program_account::<Block>(
+            block_info,
+            system_program,
+            signer_info,
+            &ore_api::ID,
+            &[BLOCK, &id.to_le_bytes()],
+        )?;
+        let block = block_info.as_account_mut::<Block>(&ore_api::ID)?;
+        block.id = id;
+        block.opener = *signer_info.key;
+        block.best_hash = [0; 32];
+        block.best_hash_miner = Pubkey::default();
+        block.reward = 0; // Set by reset instruction
+        block.start_slot = u64::MAX; // Set by reset instruction
+        block.end_slot = u64::MAX; // Set by reset instruction
+        block.slot_hash = [0; 32]; // Set by reset instruction
+        block.total_hashpower = 0;
+    } else {
+        block_info
+            .as_account_mut::<Block>(&ore_api::ID)?
+            .assert_mut(|b| b.id == id)?;
+    }
 
     Ok(())
 }