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
@@ -11810,6 +11810,11 @@
       (PreExtendType == MVT::Other))
     return SDValue();
 
+  // Restrict valid pre-extend data type
+  if (PreExtendType != MVT::i8 && PreExtendType != MVT::i16 &&
+      PreExtendType != MVT::i32)
+    return SDValue();
+
   EVT PreExtendVT = TargetType.changeVectorElementType(PreExtendType);
 
   if (PreExtendVT.getVectorElementCount() != TargetType.getVectorElementCount())
diff --git a/llvm/test/CodeGen/AArch64/aarch64-dup-ext-vectortype-crash.ll b/llvm/test/CodeGen/AArch64/aarch64-dup-ext-vectortype-crash.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/aarch64-dup-ext-vectortype-crash.ll
@@ -0,0 +1,16 @@
+; RUN: llc < %s -mtriple aarch64-none-linux-gnu | FileCheck %s
+
+; This test covers a case where extended value types can't be converted to
+; vector types, resulting in a crash. We don't care about the specific output
+; here, only that this case no longer causes said crash.
+; See https://reviews.llvm.org/D91255#2484399 for context
+define <8 x i16> @extend_i7_v8i16(i7 %src, <8 x i8> %b) {
+; CHECK-LABEL: extend_i7_v8i16:
+entry:
+    %in = sext i7 %src to i16
+    %ext.b = sext <8 x i8> %b to <8 x i16>
+    %broadcast.splatinsert = insertelement <8 x i16> undef, i16 %in, i16 0
+    %broadcast.splat = shufflevector <8 x i16> %broadcast.splatinsert, <8 x i16> undef, <8 x i32> zeroinitializer
+    %out = mul nsw <8 x i16> %broadcast.splat, %ext.b
+    ret <8 x i16> %out
+}