diff --git a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
index fe2aac78e5ab0..4bc65067473ee 100644
--- a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -391,8 +391,10 @@ static SmallBitVector isUndefVector(const Value *V,
         if (isa<T>(II->getOperand(1)))
           continue;
         std::optional<unsigned> Idx = getInsertIndex(II);
-        if (!Idx)
-          continue;
+        if (!Idx) {
+          Res.reset();
+          return Res;
+        }
         if (*Idx < UseMask.size() && !UseMask.test(*Idx))
           Res.reset(*Idx);
       }
diff --git a/llvm/test/Transforms/SLPVectorizer/X86/unknown-entries.ll b/llvm/test/Transforms/SLPVectorizer/X86/unknown-entries.ll
new file mode 100644
index 0000000000000..fc22280c2b8ad
--- /dev/null
+++ b/llvm/test/Transforms/SLPVectorizer/X86/unknown-entries.ll
@@ -0,0 +1,25 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
+; RUN: opt < %s -passes=slp-vectorizer -S | FileCheck %s
+
+target triple = "x86_64-unknown-linux-gnu"
+
+define <3 x i64> @ahyes(i64 %position, i64 %value) {
+; CHECK-LABEL: define <3 x i64> @ahyes(
+; CHECK-SAME: i64 [[POSITION:%.*]], i64 [[VALUE:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = insertelement <2 x i64> poison, i64 [[VALUE]], i32 0
+; CHECK-NEXT:    [[TMP1:%.*]] = shufflevector <2 x i64> [[TMP0]], <2 x i64> poison, <2 x i32> zeroinitializer
+; CHECK-NEXT:    [[TMP2:%.*]] = add <2 x i64> [[TMP1]], <i64 1, i64 2>
+; CHECK-NEXT:    [[TMP3:%.*]] = insertelement <3 x i64> poison, i64 [[VALUE]], i64 [[POSITION]]
+; CHECK-NEXT:    [[TMP4:%.*]] = shufflevector <2 x i64> [[TMP2]], <2 x i64> poison, <3 x i32> <i32 0, i32 1, i32 poison>
+; CHECK-NEXT:    [[TMP5:%.*]] = shufflevector <3 x i64> [[TMP3]], <3 x i64> [[TMP4]], <3 x i32> <i32 3, i32 4, i32 2>
+; CHECK-NEXT:    ret <3 x i64> [[TMP5]]
+;
+entry:
+  %0 = add i64 %value, 1
+  %1 = add i64 %value, 2
+  %2 = insertelement <3 x i64> poison, i64 %value, i64 %position
+  %3 = insertelement <3 x i64> %2, i64 %0, i64 0
+  %4 = insertelement <3 x i64> %3, i64 %1, i64 1
+  ret <3 x i64> %4
+}