diff --git a/novelwriter/core/index.py b/novelwriter/core/index.py
index c48dbb58..bdd49925 100644
--- a/novelwriter/core/index.py
+++ b/novelwriter/core/index.py
@@ -68,7 +68,7 @@ class NWIndex:
         self._indexBroken = False
 
         # TimeStamps
-        self._indexChange = 0
+        self._indexChange = 0.0
         self._rootChange = {}
 
         return
@@ -93,10 +93,22 @@ class NWIndex:
         """
         self._tagsIndex.clear()
         self._itemIndex.clear()
-        self._indexChange = 0
+        self._indexChange = 0.0
         self._rootChange = {}
         return
 
+    def rebuildIndex(self):
+        """Rebuild the entire index from scratch.
+        """
+        self.clearIndex()
+        for nwItem in self._project.tree:
+            if nwItem is not None and nwItem.isFileType():
+                tHandle = nwItem.itemHandle
+                theDoc = self._project.storage.getDocument(tHandle)
+                self.scanText(tHandle, theDoc.readDocument() or "")
+        self._indexBroken = False
+        return
+
     def deleteHandle(self, tHandle):
         """Delete all entries of a given document handle.
         """
@@ -125,13 +137,13 @@ class NWIndex:
     def indexChangedSince(self, checkTime):
         """Check if the index has changed since a given time.
         """
-        return self._indexChange > checkTime
+        return self._indexChange > float(checkTime)
 
     def rootChangedSince(self, rootHandle, checkTime):
         """Check if the index has changed since a given time for a
         given root item.
         """
-        return self._rootChange.get(rootHandle, self._indexChange) > checkTime
+        return self._rootChange.get(rootHandle, self._indexChange) > float(checkTime)
 
     ##
     #  Load and Save Index to/from File
@@ -176,7 +188,7 @@ class NWIndex:
                 logger.warning("Item '%s' is not in the index", fHandle)
                 self.reIndexHandle(fHandle)
 
-        self._indexChange = round(time())
+        self._indexChange = time()
 
         logger.debug("Index loaded in %.3f ms", (time() - tStart)*1000)
 
@@ -256,7 +268,7 @@ class NWIndex:
             self._scanActive(tHandle, theItem, theText, itemTags)
 
         # Update timestamps for index changes
-        nowTime = round(time())
+        nowTime = time()
         self._indexChange = nowTime
         self._rootChange[theItem.itemRoot] = nowTime
 
diff --git a/novelwriter/core/project.py b/novelwriter/core/project.py
index cdcb83d0..bb26ff5e 100644
--- a/novelwriter/core/project.py
+++ b/novelwriter/core/project.py
@@ -369,8 +369,11 @@ class NWProject(QObject):
 
         self._scanProjectFolder()
         self._index.loadIndex()
-        self.updateWordCounts()
+        if xmlReader.state == XMLReadState.WAS_LEGACY:
+            # Often, the index needs to be rebuilt when updating format
+            self._index.rebuildIndex()
 
+        self.updateWordCounts()
         self._projOpened = time()
         self._projAltered = False
 
diff --git a/novelwriter/guimain.py b/novelwriter/guimain.py
index 20f7ce2d..56ba564f 100644
--- a/novelwriter/guimain.py
+++ b/novelwriter/guimain.py
@@ -833,17 +833,8 @@ class GuiMain(QMainWindow):
         tStart = time()
 
         self.projView.saveProjectTasks()
-        self.theProject.index.clearIndex()
-
-        for tItem in self.theProject.tree:
-            if tItem is None:  # pragma: no cover
-                continue  # This is a bug trap
-
-            logger.debug("Indexing '%s'", tItem.itemName)
-            if self.theProject.index.reIndexHandle(tItem.itemHandle):
-                # Update Word Counts
-                self.projView.propagateCount(tItem.itemHandle, tItem.wordCount, countChildren=True)
-                self.projView.setTreeItemValues(tItem.itemHandle)
+        self.theProject.index.rebuildIndex()
+        self.projView.populateTree()
 
         tEnd = time()
         self.setStatus(
diff --git a/tests/test_core/test_core_index.py b/tests/test_core/test_core_index.py
index 82bf53c8..6d85dfb0 100644
--- a/tests/test_core/test_core_index.py
+++ b/tests/test_core/test_core_index.py
@@ -90,7 +90,7 @@ def testCoreIndex_LoadSave(monkeypatch, prjLipsum, mockGUI, tstPaths):
     assert theIndex._tagsIndex._tags == {}
     assert theIndex._itemIndex._items == {}
 
-    # No folder for sloading
+    # No folder for loading
     with monkeypatch.context() as mp:
         mp.setattr("novelwriter.core.storage.NWStorage.getMetaFile", lambda *a: None)
         assert theIndex.loadIndex() is False
@@ -108,6 +108,13 @@ def testCoreIndex_LoadSave(monkeypatch, prjLipsum, mockGUI, tstPaths):
     assert str(theIndex._tagsIndex.packData()) == tagIndex
     assert str(theIndex._itemIndex.packData()) == itemsIndex
 
+    # Rebuild index
+    theIndex.clearIndex()
+    theIndex.rebuildIndex()
+
+    assert str(theIndex._tagsIndex.packData()) == tagIndex
+    assert str(theIndex._itemIndex.packData()) == itemsIndex
+
     # Check File
     copyfile(projFile, testFile)
     assert cmpFiles(testFile, compFile)
diff --git a/tests/test_core/test_core_project.py b/tests/test_core/test_core_project.py
index d2931fd8..1f3dc73e 100644
--- a/tests/test_core/test_core_project.py
+++ b/tests/test_core/test_core_project.py
@@ -230,7 +230,7 @@ def testCoreProject_Open(monkeypatch, caplog, mockGUI, fncPath, mockRnd):
         assert "The file format of your project is about to be" in mockGUI.lastQuestion[1]
         mockGUI.askResponse = True
 
-    # Won't convert legacy file
+    # Won't open project from newer version
     with monkeypatch.context() as mp:
         mp.setattr(ProjectXMLReader, "hexVersion", property(lambda *a: 0x99999999))
         mockGUI.askResponse = False
@@ -245,6 +245,18 @@ def testCoreProject_Open(monkeypatch, caplog, mockGUI, fncPath, mockRnd):
 
     assert theProject.closeProject()
 
+    # Trigger an index rebuild
+    with monkeypatch.context() as mp:
+        mp.setattr(ProjectXMLReader, "state", property(lambda *a: XMLReadState.WAS_LEGACY))
+        mp.setattr("novelwriter.core.index.NWIndex.loadIndex", lambda *a: True)
+        mockGUI.askResponse = True
+        theProject.index._indexBroken = True
+        assert theProject.openProject(fncPath) is True
+        assert "The file format of your project is about to be" in mockGUI.lastQuestion[1]
+        assert theProject.index._indexBroken is False
+
+    assert theProject.closeProject()
+
 # END Test testCoreProject_Open