diff --git a/api/src/handlers.rs b/api/src/handlers.rs
index e491ac7dc..1bd37dc8c 100644
--- a/api/src/handlers.rs
+++ b/api/src/handlers.rs
@@ -120,7 +120,7 @@ impl UtxoHandler {
 		let outputs = block
 			.outputs
 			.iter()
-			.filter(|c|self.chain.is_unspent(&c.commit).unwrap())
+			.filter(|c|self.chain.is_unspent(&c.commit, &c.switch_commit_hash).unwrap())
 			.map(|k|OutputSwitch::from_output(k, &header))
 			.collect();
 		BlockOutputs {
diff --git a/chain/src/chain.rs b/chain/src/chain.rs
index 3b46e57b0..04ee2d977 100644
--- a/chain/src/chain.rs
+++ b/chain/src/chain.rs
@@ -23,7 +23,7 @@ use util::secp::pedersen::{Commitment, RangeProof};
 use core::core::SumCommit;
 use core::core::pmmr::{HashSum, NoSum};
 
-use core::core::{Block, BlockHeader, Output, TxKernel};
+use core::core::{Block, BlockHeader, Output, TxKernel, SwitchCommitHash};
 use core::core::target::Difficulty;
 use core::core::hash::Hash;
 use grin_store::Error::NotFoundErr;
@@ -360,21 +360,26 @@ impl Chain {
 	/// way that's consistent with the current chain state and more
 	/// specifically the current winning fork.
 	pub fn get_unspent(&self, output_ref: &Commitment) -> Result<Output, Error> {
-		let sumtrees = self.sumtrees.read().unwrap();
-		let is_unspent = sumtrees.is_unspent(output_ref)?;
-		if is_unspent {
-			self.store
-				.get_output_by_commit(output_ref)
-				.map_err(|e| Error::StoreErr(e, "chain get unspent".to_owned()))
-		} else {
-			Err(Error::OutputNotFound)
+		match self.store.get_output_by_commit(output_ref) {
+			Ok(out) => {
+				let mut sumtrees = self.sumtrees.write().unwrap();
+				if sumtrees.is_unspent(output_ref, &out.switch_commit_hash())? {
+					Ok(out)
+				} else {
+					Err(Error::OutputNotFound)
+				}
+			}
+			Err(NotFoundErr) => Err(Error::OutputNotFound),
+			Err(e) => Err(Error::StoreErr(e, "chain get unspent".to_owned())),
 		}
 	}
 
 	/// Checks whether an output is unspent
-	pub fn is_unspent(&self, output_ref: &Commitment) -> Result<bool, Error> {
-		let sumtrees = self.sumtrees.read().unwrap();
-		sumtrees.is_unspent(output_ref)
+	pub fn is_unspent(&self, output_ref: &Commitment, switch: &SwitchCommitHash)
+		-> Result<bool, Error> {
+
+		let mut sumtrees = self.sumtrees.write().unwrap();
+		sumtrees.is_unspent(output_ref, switch)
 	}
 
 	/// Sets the sumtree roots on a brand new block by applying the block on the
diff --git a/chain/src/sumtree.rs b/chain/src/sumtree.rs
index 872d86d3b..28ea0017a 100644
--- a/chain/src/sumtree.rs
+++ b/chain/src/sumtree.rs
@@ -22,8 +22,8 @@ use std::sync::Arc;
 
 use util::secp::pedersen::{RangeProof, Commitment};
 
-use core::core::{Block, SumCommit, TxKernel};
-use core::core::pmmr::{Backend, HashSum, NoSum, Summable, PMMR};
+use core::core::{Block, SumCommit, SwitchCommitHash, TxKernel};
+use core::core::pmmr::{HashSum, NoSum, Summable, PMMR};
 use core::core::hash::Hashed;
 use grin_store;
 use grin_store::sumtree::PMMRBackend;
@@ -90,16 +90,22 @@ impl SumTrees {
 	}
 
 	/// Whether a given commitment exists in the Output MMR and it's unspent
-	pub fn is_unspent(&self, commit: &Commitment) -> Result<bool, Error> {
+	pub fn is_unspent(&mut self, commit: &Commitment, switch: &SwitchCommitHash)
+		-> Result<bool, Error> {
+
 		let rpos = self.commit_index.get_output_pos(commit);
 		match rpos {
 			Ok(pos) => {
-				// checking the position is within the MMR, the commit index could be
-				// returning rewound data
-				if pos > self.output_pmmr_h.last_pos {
-					Ok(false)
+				let output_pmmr = PMMR::at(
+					&mut self.output_pmmr_h.backend,
+					self.output_pmmr_h.last_pos
+				);
+				if let Some(hs) = output_pmmr.get(pos) {
+					let hashsum = HashSum::from_summable(
+						pos, &SumCommit{commit: commit.clone()}, Some(switch));
+					Ok(hs.hash == hashsum.hash)
 				} else {
-					Ok(self.output_pmmr_h.backend.get(pos).is_some())
+					Ok(false)
 				}
 			}
 			Err(grin_store::Error::NotFoundErr) => Ok(false),