diff --git a/lib/Analysis/PostDominators.cpp b/lib/Analysis/PostDominators.cpp
index 48f7b30866f..1188cff0303 100644
--- a/lib/Analysis/PostDominators.cpp
+++ b/lib/Analysis/PostDominators.cpp
@@ -112,8 +112,12 @@ void PostDominatorTree::calculate(Function &F) {
   // relationships.  These blocks, which have no successors, end with return and
   // unwind instructions.
   for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
-    if (succ_begin(I) == succ_end(I))
-      Roots.push_back(I);
+    if (succ_begin(I) == succ_end(I)) {
+      Instruction *Insn = I->getTerminator();
+      // Unreachable block is not a root node.
+      if (!isa<UnreachableInst>(Insn))
+        Roots.push_back(I);
+    }
   
   Vertex.push_back(0);
   
diff --git a/test/Transforms/ADCE/2007-07-23-InfiniteLoop.ll b/test/Transforms/ADCE/2007-07-23-InfiniteLoop.ll
new file mode 100644
index 00000000000..f3500ed7e18
--- /dev/null
+++ b/test/Transforms/ADCE/2007-07-23-InfiniteLoop.ll
@@ -0,0 +1,13 @@
+; RUN: llvm-as < %s |   opt -adce | llvm-dis | grep switch
+; PR 1564
+  
+define fastcc void @out() {
+    start:
+            br label %loop
+    unreachable:
+            unreachable
+    loop:
+            switch i32 0, label %unreachable [
+                     i32 0, label %loop
+            ]
+}