diff --git a/lib/blocks.js b/lib/blocks.js
index 51417e5..d922d43 100644
--- a/lib/blocks.js
+++ b/lib/blocks.js
@@ -27,6 +27,7 @@ BlockController.prototype.block = function(req, res, next, hash) {
     }
 
     var info = self.node.services.bitcoind.getBlockIndex(hash);
+    info.isMainChain = self.node.services.bitcoind.isMainChain(hash);
 
     req.block = self.transformBlock(block, info);
     next();
@@ -54,8 +55,8 @@ BlockController.prototype.transformBlock = function(block, info) {
     previousblockhash: blockObj.header.prevHash,
     nextblockhash: null, // placeholder
     reward: this.getBlockReward(info.height) / 1e8,
-    isMainChain: true // placeholder
-  }
+    isMainChain: info.isMainChain
+  };
 };
 
 /**
diff --git a/test/blocks.js b/test/blocks.js
index 655e555..4eab00a 100644
--- a/test/blocks.js
+++ b/test/blocks.js
@@ -74,7 +74,8 @@ describe('Blocks', function() {
       getBlock: sinon.stub().callsArgWith(1, null, bitcoreBlock),
       services: {
         bitcoind: {
-          getBlockIndex: sinon.stub().returns(blockIndexes['0000000000000afa0c3c0afd450c793a1e300ec84cbe9555166e06132f19a8f7'])
+          getBlockIndex: sinon.stub().returns(blockIndexes['0000000000000afa0c3c0afd450c793a1e300ec84cbe9555166e06132f19a8f7']),
+          isMainChain: sinon.stub().returns(true)
         },
         db: {
           tip: {