diff --git a/ethereum/blocks.py b/ethereum/blocks.py
index e7d12009d..35b5968c0 100644
--- a/ethereum/blocks.py
+++ b/ethereum/blocks.py
@@ -446,6 +446,9 @@ def __init__(self, header, transaction_list=[], uncles=[], env=None,
             if self.timestamp >= 2 ** 256:
                 raise ValueError("Timestamp waaaaaaaaaaayy too large")
 
+        if self.gas_limit > 2 ** 63 - 1:
+            raise ValueError("Block's gaslimit went too high!")
+
         for uncle in uncles:
             assert isinstance(uncle, BlockHeader)