diff --git a/lib/Analysis/RegionInfo.cpp b/lib/Analysis/RegionInfo.cpp
index 27cee76e081..abc057a773a 100644
--- a/lib/Analysis/RegionInfo.cpp
+++ b/lib/Analysis/RegionInfo.cpp
@@ -136,14 +136,16 @@ bool Region::isSimple() const {
     return false;
 
   for (pred_iterator PI = pred_begin(entry), PE = pred_end(entry); PI != PE;
-       ++PI)
-    if (!contains(*PI)) {
+       ++PI) {
+    BasicBlock *Pred = *PI;
+    if (DT->getNode(Pred) && !contains(Pred)) {
       if (found) {
         isSimple = false;
         break;
       }
       found = true;
     }
+  }
 
   found = false;
 
diff --git a/test/Analysis/RegionInfo/20100809_bb_not_in_domtree.ll b/test/Analysis/RegionInfo/20100809_bb_not_in_domtree.ll
new file mode 100644
index 00000000000..218b4375f70
--- /dev/null
+++ b/test/Analysis/RegionInfo/20100809_bb_not_in_domtree.ll
@@ -0,0 +1,20 @@
+; RUN: opt -regions %s
+define i32 @main() nounwind {
+entry:
+  br label %for.cond
+
+test:
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.inc, %entry
+  br i1 true, label %for.body, label %for.end
+
+for.body:                                         ; preds = %for.cond
+  br label %for.inc
+
+for.inc:                                          ; preds = %for.body
+  br label %for.cond
+
+for.end:                                          ; preds = %for.cond
+  ret i32 0
+}