diff --git a/OP_RETURN.py b/OP_RETURN.py
index 594bc8d..69fc721 100644
--- a/OP_RETURN.py
+++ b/OP_RETURN.py
@@ -55,6 +55,7 @@
 
 OP_RETURN_NET_TIMEOUT=10 # how long to time out (in seconds) when communicating with bitcoin node
 
+SAT = 100000000 # coin divisible by how many satoshis
 
 # User-facing functions
 
@@ -149,7 +150,9 @@ def OP_RETURN_store(data, testnet=False):
 		# Some preparation for this iteration
 	
 		last_txn=((data_ptr+OP_RETURN_MAX_BYTES)>=data_len) # is this the last tx in the chain?
-		change_amount=input_amount-OP_RETURN_BTC_FEE
+		change_amount = (
+			int(input_amount * SAT) - int(OP_RETURN_BTC_FEE * SAT)
+			) / SAT
 		metadata=data[data_ptr:data_ptr+OP_RETURN_MAX_BYTES]
 			
 		# Build and send this transaction