Index: include/llvm/Support/GenericDomTreeConstruction.h
===================================================================
--- include/llvm/Support/GenericDomTreeConstruction.h
+++ include/llvm/Support/GenericDomTreeConstruction.h
@@ -1297,9 +1297,12 @@
         errs().flush();
         return false;
       }
+
+      return true;
     }
 
-    RootsT ComputedRoots = FindRoots(DT, nullptr);
+    // Check PostDomTree roots.
+    const RootsT ComputedRoots = FindRoots(DT, nullptr);
     if (DT.Roots.size() != ComputedRoots.size() ||
         !std::is_permutation(DT.Roots.begin(), DT.Roots.end(),
                              ComputedRoots.begin())) {
@@ -1314,6 +1317,21 @@
       return false;
     }
 
+    for (const NodePtr Root : ComputedRoots) {
+      const TreeNodePtr TN = DT.getNode(Root);
+      if (!TN) {
+        errs() << "Computed root: " << BlockNamePrinter(Root)
+               << " not found in the PostDomTree!\n";
+        return false;
+      }
+
+      if (!DT.isVirtualRoot(TN->getIDom())) {
+        errs() << "Computed root: " << BlockNamePrinter(TN)
+               << " is not connected to the virtual root!\n";
+        return false;
+      }
+    }
+
     return true;
   }