diff --git a/core/block.js b/core/block.js
index b0ff7a598..765437e19 100644
--- a/core/block.js
+++ b/core/block.js
@@ -691,8 +691,6 @@ Blockly.Block.prototype.setNextStatement = function(newBoolean, opt_check) {
     this.nextConnection = null;
   }
   if (newBoolean) {
-    goog.asserts.assert(!this.outputConnection,
-        'Remove output connection prior to adding previous connection.');
     if (opt_check === undefined) {
       opt_check = null;
     }
@@ -721,8 +719,8 @@ Blockly.Block.prototype.setOutput = function(newBoolean, opt_check) {
     this.outputConnection = null;
   }
   if (newBoolean) {
-    goog.asserts.assert(!this.previousConnection && !this.nextConnection,
-        'Remove previous/next connection prior to adding output connection.');
+    goog.asserts.assert(!this.previousConnection,
+        'Remove previous connection prior to adding output connection.');
     if (opt_check === undefined) {
       opt_check = null;
     }
@@ -889,9 +887,8 @@ Blockly.Block.prototype.appendDummyInput = function(opt_name) {
 Blockly.Block.prototype.jsonInit = function(json) {
   // Validate inputs.
   goog.asserts.assert(json['output'] == undefined ||
-      (json['previousStatement'] == undefined &&
-      json['nextStatement'] == undefined),
-      'Must not have both an output and a previous/nextStatement.');
+      json['previousStatement'] == undefined,
+      'Must not have both an output and a previousStatement.');
 
   // Set basic properties of block.
   this.setColour(json['colour']);