diff --git a/llvm/include/llvm/IR/Instructions.h b/llvm/include/llvm/IR/Instructions.h
--- a/llvm/include/llvm/IR/Instructions.h
+++ b/llvm/include/llvm/IR/Instructions.h
@@ -3942,6 +3942,9 @@
             ArrayRef<BasicBlock *> IndirectDests, ArrayRef<Value *> Args,
             ArrayRef<OperandBundleDef> Bundles, const Twine &NameStr);
 
+  /// Should the Indirect Destinations change, scan + update the Arg list.
+  void updateArgBlockAddresses(unsigned i, BasicBlock *B);
+
   /// Compute the number of operands to allocate.
   static int ComputeNumOperands(int NumArgs, int NumIndirectDests,
                                 int NumBundleInputs = 0) {
@@ -4079,7 +4082,7 @@
     return cast<BasicBlock>(*(&Op<-1>() - getNumIndirectDests() - 1));
   }
   BasicBlock *getIndirectDest(unsigned i) const {
-    return cast<BasicBlock>(*(&Op<-1>() - getNumIndirectDests() + i));
+    return cast_or_null<BasicBlock>(*(&Op<-1>() - getNumIndirectDests() + i));
   }
   SmallVector<BasicBlock *, 16> getIndirectDests() const {
     SmallVector<BasicBlock *, 16> IndirectDests;
@@ -4091,6 +4094,7 @@
     *(&Op<-1>() - getNumIndirectDests() - 1) = reinterpret_cast<Value *>(B);
   }
   void setIndirectDest(unsigned i, BasicBlock *B) {
+    updateArgBlockAddresses(i, B);
     *(&Op<-1>() - getNumIndirectDests() + i) = reinterpret_cast<Value *>(B);
   }
 
@@ -4100,11 +4104,10 @@
     return i == 0 ? getDefaultDest() : getIndirectDest(i - 1);
   }
 
-  void setSuccessor(unsigned idx, BasicBlock *NewSucc) {
-    assert(idx < getNumIndirectDests() + 1 &&
+  void setSuccessor(unsigned i, BasicBlock *NewSucc) {
+    assert(i < getNumIndirectDests() + 1 &&
            "Successor # out of range for callbr!");
-    *(&Op<-1>() - getNumIndirectDests() -1 + idx) =
-        reinterpret_cast<Value *>(NewSucc);
+    return i == 0 ? setDefaultDest(NewSucc) : setIndirectDest(i - 1, NewSucc);
   }
 
   unsigned getNumSuccessors() const { return getNumIndirectDests() + 1; }
diff --git a/llvm/lib/IR/Instructions.cpp b/llvm/lib/IR/Instructions.cpp
--- a/llvm/lib/IR/Instructions.cpp
+++ b/llvm/lib/IR/Instructions.cpp
@@ -822,6 +822,17 @@
   setName(NameStr);
 }
 
+void CallBrInst::updateArgBlockAddresses(unsigned i, BasicBlock *B) {
+  assert(getNumIndirectDests() > i && "IndirectDest # out of range for callbr");
+  if (BasicBlock *OldBB = getIndirectDest(i)) {
+    BlockAddress *Old = BlockAddress::get(OldBB);
+    BlockAddress *New = BlockAddress::get(B);
+    for (unsigned ArgNo = 0, e = getNumArgOperands(); ArgNo != e; ++ArgNo)
+      if (dyn_cast<BlockAddress>(getArgOperand(ArgNo)) == Old)
+        setArgOperand(ArgNo, New);
+  }
+}
+
 CallBrInst::CallBrInst(const CallBrInst &CBI)
     : CallBase(CBI.Attrs, CBI.FTy, CBI.getType(), Instruction::CallBr,
                OperandTraits<CallBase>::op_end(this) - CBI.getNumOperands(),
diff --git a/llvm/unittests/IR/InstructionsTest.cpp b/llvm/unittests/IR/InstructionsTest.cpp
--- a/llvm/unittests/IR/InstructionsTest.cpp
+++ b/llvm/unittests/IR/InstructionsTest.cpp
@@ -1061,5 +1061,56 @@
   FNeg->deleteValue();
 }
 
+TEST(InstructionsTest, CallBrInstruction) {
+  LLVMContext Context;
+  std::unique_ptr<Module> M = parseIR(Context, R"(
+define void @foo() {
+entry:
+  callbr void asm sideeffect "// XXX: ${0:l}", "X"(i8* blockaddress(@foo, %branch_test.exit))
+          to label %land.rhs.i [label %branch_test.exit]
+
+land.rhs.i:
+  br label %branch_test.exit
+
+branch_test.exit:
+  %0 = phi i1 [ true, %entry ], [ false, %land.rhs.i ]
+  br i1 %0, label %if.end, label %if.then
+
+if.then:
+  ret void
+
+if.end:
+  ret void
+}
+)");
+  Function *Foo = M->getFunction("foo");
+  auto BBs = Foo->getBasicBlockList().begin();
+  CallBrInst &CBI = cast<CallBrInst>(BBs->front());
+  ++BBs;
+  ++BBs;
+  BasicBlock &BranchTestExit = *BBs;
+  ++BBs;
+  BasicBlock &IfThen = *BBs;
+
+  // Test that setting the first indirect destination of callbr updates the dest
+  EXPECT_EQ(&BranchTestExit, CBI.getIndirectDest(0));
+  CBI.setIndirectDest(0, &IfThen);
+  EXPECT_EQ(&IfThen, CBI.getIndirectDest(0));
+
+  // Further, test that changing the indirect destination updates the arg
+  // operand to use the block address of the new indirect destination basic
+  // block. This is a critical invariant of CallBrInst.
+  BlockAddress *IndirectBA = BlockAddress::get(CBI.getIndirectDest(0));
+  BlockAddress *ArgBA = cast<BlockAddress>(CBI.getArgOperand(0));
+  EXPECT_EQ(IndirectBA, ArgBA)
+      << "After setting the indirect destination, callbr had an indirect "
+         "destination of '"
+      << CBI.getIndirectDest(0)->getName() << "', but a argument of '"
+      << ArgBA->getBasicBlock()->getName() << "'. These should always match:\n"
+      << CBI;
+  EXPECT_EQ(IndirectBA->getBasicBlock(), &IfThen);
+  EXPECT_EQ(ArgBA->getBasicBlock(), &IfThen);
+}
+
 } // end anonymous namespace
 } // end namespace llvm