diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -7371,7 +7371,8 @@
         VectorTy =
             largestIntegerVectorType(ToVectorTy(I->getType(), VF), MinVecTy);
       } else if (Opcode == Instruction::ZExt || Opcode == Instruction::SExt) {
-        SrcVecTy = largestIntegerVectorType(SrcVecTy, MinVecTy);
+        // Leave SrcVecTy unchanged - we only shrink the destination element
+        // type.
         VectorTy =
             smallestIntegerVectorType(ToVectorTy(I->getType(), VF), MinVecTy);
       }
diff --git a/llvm/test/Transforms/LoopVectorize/AArch64/type-shrinkage-zext-costs.ll b/llvm/test/Transforms/LoopVectorize/AArch64/type-shrinkage-zext-costs.ll
--- a/llvm/test/Transforms/LoopVectorize/AArch64/type-shrinkage-zext-costs.ll
+++ b/llvm/test/Transforms/LoopVectorize/AArch64/type-shrinkage-zext-costs.ll
@@ -16,7 +16,8 @@
 ; CHECK-COST: LV: Found an estimated cost of 1 for VF vscale x 1 For instruction:   %conv = zext i8 %0 to i32
 ; CHECK-COST: LV: Found an estimated cost of 1 for VF vscale x 2 For instruction:   %conv = zext i8 %0 to i32
 ; CHECK-COST: LV: Found an estimated cost of 1 for VF vscale x 4 For instruction:   %conv = zext i8 %0 to i32
-; CHECK-COST: LV: Found an estimated cost of 1 for VF vscale x 8 For instruction:   %conv = zext i8 %0 to i32
+; CHECK-COST: LV: Found an estimated cost of 0 for VF vscale x 8 For instruction:   %conv = zext i8 %0 to i32
+
 ; CHECK-LABEL: define void @zext_i8_i16
 ; CHECK-SAME: (ptr noalias nocapture readonly [[P:%.*]], ptr noalias nocapture [[Q:%.*]], i32 [[LEN:%.*]]) #[[ATTR0:[0-9]+]] {
 ; CHECK-NEXT:  entry:
@@ -99,7 +100,8 @@
 ; CHECK-COST: LV: Found an estimated cost of 1 for VF vscale x 1 For instruction:   %conv = sext i8 %0 to i32
 ; CHECK-COST: LV: Found an estimated cost of 1 for VF vscale x 2 For instruction:   %conv = sext i8 %0 to i32
 ; CHECK-COST: LV: Found an estimated cost of 1 for VF vscale x 4 For instruction:   %conv = sext i8 %0 to i32
-; CHECK-COST: LV: Found an estimated cost of 1 for VF vscale x 8 For instruction:   %conv = sext i8 %0 to i32
+; CHECK-COST: LV: Found an estimated cost of 0 for VF vscale x 8 For instruction:   %conv = sext i8 %0 to i32
+
 ; CHECK-LABEL: define void @sext_i8_i16
 ; CHECK-SAME: (ptr noalias nocapture readonly [[P:%.*]], ptr noalias nocapture [[Q:%.*]], i32 [[LEN:%.*]]) #[[ATTR0]] {
 ; CHECK-NEXT:  entry: