diff --git a/framework/DataObjects/TestXHistorySet.py b/framework/DataObjects/TestXHistorySet.py
index 4ed2f62d46..e6e9e99999 100644
--- a/framework/DataObjects/TestXHistorySet.py
+++ b/framework/DataObjects/TestXHistorySet.py
@@ -644,6 +644,44 @@ def formatRealization(rlz):
 checkRlz('No input space',rlz0,rlz,skip='Timelike')
 
 
+
+######################################
+#           ASYNC HISTORIES          #
+######################################
+xml = createElement('HistorySet',attrib={'name':'test'})
+xml.append(createElement('Input',text='a,b'))
+xml.append(createElement('Output',text='x,y'))
+data = XHistorySet.HistorySet()
+data.messageHandler = mh
+data._readMoreXML(xml)
+rlz1 = {'a': np.array([1.0]),
+        'b': np.array([2.0]),
+        'x': np.array([1.0, 2.0, 3.0]),
+        'y': np.array([6.0, 7.0, 8.0]),
+        'time': np.array([0.0, 0.1, 0.2])}
+
+rlz2 = {'a': np.array([11.0]),
+        'b': np.array([12.0]),
+        'x': np.array([11.0, 12.0]),
+        'y': np.array([16.0, 17.0]),
+        'time': np.array([0.05, 0.15])}
+
+data.addRealization(rlz1)
+data.addRealization(rlz2)
+# check collection in realizations, in collector
+checkRlz('Adding asynchronous histories, collector[0]',data.realization(index=0),rlz1,skip=['time'])
+checkRlz('Adding asynchronous histories, collector[1]',data.realization(index=1),rlz2,skip=['time'])
+# check stored in collector, not in synced histories
+idx = data._orderedVars.index('time')
+times = data._collector[:,idx]
+checkArray('Asynchronous histories, collector, time[0]',times[0],rlz1['time'],float)
+checkArray('Asynchronous histories, collector, time[1]',times[1],rlz2['time'],float)
+# check as dataset, just for kicks
+data.asDataset()
+checkRlz('Adding asynchronous histories, dataset[0]',data.realization(index=0),rlz1,skip=['time'])
+checkRlz('Adding asynchronous histories, dataset[1]',data.realization(index=1),rlz2,skip=['time'])
+
+
 print(results)
 
 sys.exit(results["fail"])
diff --git a/framework/DataObjects/XDataSet.py b/framework/DataObjects/XDataSet.py
index a7c7de4553..370279252c 100644
--- a/framework/DataObjects/XDataSet.py
+++ b/framework/DataObjects/XDataSet.py
@@ -162,7 +162,7 @@ def addRealization(self,rlz):
     rlz = self._selectiveRealization(rlz)
 
     ## check alignment of indexes
-    self._checkAlignedIndexes(rlz) # TODO implement
+    self._checkAlignedIndexes(rlz)
     #  NB If no scalar entry is made, this construction fails.  In that case,
     #  instead of treating each dataarrray as an object, numpy.asarray calls their asarray methods,
     #  unfolding them and making a full numpy array with more dimensions, instead of effectively
@@ -689,11 +689,17 @@ def _checkAlignedIndexes(self,rlz,tol=1e-15):
     for index in self.indexes:
       # if it's aligned so far, check if it still is
       if index in self._alignedIndexes.keys():
-        # if close enough, then keep the aligned values; otherwise, take action
-        if isinstance(rlz[index][0],(float,int)):
-          closeEnough = all(np.isclose(rlz[index],self._alignedIndexes[index],rtol=tol))
+        # first, if lengths don't match, they're not aligned.
+        # TODO there are concerns this check may slow down runs; it should be profiled along with other bottlenecks to optimize our efforts.
+        if len(rlz[index]) != len(self._alignedIndexes[index]):
+          closeEnough = False
         else:
-          closeEnough = all(rlz[index] == self._alignedIndexes[index])
+          # "close enough" if float/int, otherwise require exactness
+          if isinstance(rlz[index][0],(float,int)):
+            closeEnough = all(np.isclose(rlz[index],self._alignedIndexes[index],rtol=tol))
+          else:
+            closeEnough = all(rlz[index] == self._alignedIndexes[index])
+        # if close enough, then keep the aligned values; otherwise, take action
         if not closeEnough:
           dtype = rlz[index].dtype
           # TODO add new column to collector, propagate values up to (not incl) current rlz