diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
--- a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -11831,6 +11831,11 @@
       PreExtendType != MVT::i32)
     return SDValue();
 
+  bool IsAssert =
+      ExtendOpcode == ISD::AssertSext || ExtendOpcode == ISD::AssertZext;
+  if (IsAssert && Extend.getValueType() == MVT::i64)
+    return SDValue();
+
   EVT PreExtendVT = TargetType.changeVectorElementType(PreExtendType);
 
   if (PreExtendVT.getVectorElementCount() != TargetType.getVectorElementCount())
diff --git a/llvm/test/CodeGen/AArch64/aarch64-dup-ext-crash.ll b/llvm/test/CodeGen/AArch64/aarch64-dup-ext-crash.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/aarch64-dup-ext-crash.ll
@@ -0,0 +1,33 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s -o -| FileCheck %s
+
+target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
+target triple = "aarch64-unknown-linux-gnu"
+
+; This test covers a case where an AArch64 DUP instruction is generated with an
+; invalid encoding, resulting in a crash. We don't care about the specific output
+; here, only that this case no longer causes said crash.
+define dso_local i32 @dupext_crashtest(i32 %e) local_unnamed_addr {
+; CHECK-LABEL: dupext_crashtest:
+for.body.lr.ph:
+  %conv314 = zext i32 %e to i64
+  br label %vector.memcheck
+
+vector.memcheck:                                  ; preds = %for.body.lr.ph
+  br label %vector.ph
+
+vector.ph:                                        ; preds = %vector.memcheck
+  %broadcast.splatinsert = insertelement <2 x i64> poison, i64 %conv314, i32 0
+  %broadcast.splat = shufflevector <2 x i64> %broadcast.splatinsert, <2 x i64> poison, <2 x i32> zeroinitializer
+  br label %vector.body
+
+vector.body:                                      ; preds = %vector.body, %vector.ph
+  %wide.load = load <2 x i32>, <2 x i32>* undef, align 4
+  %0 = zext <2 x i32> %wide.load to <2 x i64>
+  %1 = mul nuw <2 x i64> %broadcast.splat, %0
+  %2 = trunc <2 x i64> %1 to <2 x i32>
+  %3 = select <2 x i1> undef, <2 x i32> undef, <2 x i32> %2
+  %4 = bitcast i32* undef to <2 x i32>*
+  store <2 x i32> %3, <2 x i32>* %4, align 4
+  br label %vector.body
+}
\ No newline at end of file