diff --git a/llvm/lib/Transforms/Scalar/LoopInterchange.cpp b/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
--- a/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
@@ -1470,6 +1470,13 @@
       PHINode *NewPhi = dyn_cast<PHINode>(P.clone());
       NewPhi->setIncomingValue(0, P.getIncomingValue(0));
       NewPhi->setIncomingBlock(0, OuterLatch);
+      // We might have incoming edges from other BBs, i.e., the original outer
+      // header.
+      for (auto *Pred : predecessors(InnerLatch)) {
+        if (Pred == OuterLatch)
+          continue;
+        NewPhi->addIncoming(P.getIncomingValue(0), Pred);
+      }
       NewPhi->insertBefore(InnerLatch->getFirstNonPHI());
       P.setIncomingValue(0, NewPhi);
     }
diff --git a/llvm/test/Transforms/LoopInterchange/lcssa.ll b/llvm/test/Transforms/LoopInterchange/lcssa.ll
--- a/llvm/test/Transforms/LoopInterchange/lcssa.ll
+++ b/llvm/test/Transforms/LoopInterchange/lcssa.ll
@@ -298,3 +298,35 @@
 for.end16:                                        ; preds = %for.exit
   ret void
 }
+
+; Should not crash when the outer header branches to
+; both the inner loop and the outer latch, and there
+; is an lcssa phi node outside the loopnest.
+; REMARK: Interchanged
+; REMARK-NEXT: lcssa_08
+define i64 @lcssa_08([100 x [100 x i64]]* %Arr) {
+entry:
+  br label %for1.header
+
+for1.header:                                         ; preds = %for1.inc, %entry
+  %indvars.iv23 = phi i64 [ 0, %entry ], [ %indvars.iv.next24, %for1.inc ]
+  br i1 undef, label %for2, label %for1.inc
+
+for2:                                        ; preds = %for2, %for1.header
+  %indvars.iv = phi i64 [ 0, %for1.header ], [ %indvars.iv.next.3, %for2 ]
+  %arrayidx = getelementptr inbounds [100 x [100 x i64]], [100 x [100 x i64]]* %Arr, i64 0, i64 %indvars.iv, i64 %indvars.iv23
+  %lv = load i64, i64* %arrayidx, align 4
+  %indvars.iv.next.3 = add nuw nsw i64 %indvars.iv, 1
+  %exit1 = icmp eq i64 %indvars.iv.next.3, 100
+  br i1 %exit1, label %for1.inc, label %for2
+
+for1.inc:                                ; preds = %for2, %for1.header
+  %indvars.iv.next24 = add nuw nsw i64 %indvars.iv23, 1
+  %exit2 = icmp eq i64 %indvars.iv.next24, 100
+  br i1 %exit2, label %for1.loopexit, label %for1.header
+
+for1.loopexit:                                 ; preds = %for1.inc
+  %sum.outer.lcssa = phi i64 [ %indvars.iv23, %for1.inc ]
+  ret i64 %sum.outer.lcssa
+}
+