diff --git a/program/src/mine.rs b/program/src/mine.rs
index f6d8124..2ce35e3 100644
--- a/program/src/mine.rs
+++ b/program/src/mine.rs
@@ -41,5 +41,8 @@ pub fn process_mine(accounts: &[AccountInfo<'_>], data: &[u8]) -> ProgramResult
         block.best_hash_miner = *miner_info.key;
     }
 
+    // Only allow miners to submit 1 hash per block.
+    miner.hashpower = 0;
+
     Ok(())
 }