diff --git a/llvm/lib/IR/Verifier.cpp b/llvm/lib/IR/Verifier.cpp
--- a/llvm/lib/IR/Verifier.cpp
+++ b/llvm/lib/IR/Verifier.cpp
@@ -5311,24 +5311,40 @@
     VectorType *SubVecTy = cast<VectorType>(SubVec->getType());
     VectorType *ResultTy = cast<VectorType>(Call.getType());
 
+    ElementCount VecEC = VecTy->getElementCount();
+    ElementCount SubVecEC = SubVecTy->getElementCount();
+
     Assert(VecTy == ResultTy,
            "experimental_vector_insert vector type must match result type.");
     Assert(VecTy->getElementType() == SubVecTy->getElementType(),
            "experimental_vector_insert parameters must have the same element "
            "type.",
            &Call);
-    Assert(IdxN % SubVecTy->getElementCount().getKnownMinValue() == 0,
+    Assert(IdxN % SubVecEC.getKnownMinValue() == 0,
            "experimental_vector_insert index must be a constant multiple of "
            "the subvector's known minimum vector length.");
+
+    // If this insertion is not the 'mixed' case where a fixed vector is
+    // inserted into a scalable vector.
+    if (VecEC.isScalable() == SubVecEC.isScalable()) {
+      Assert(
+          IdxN + SubVecEC.getKnownMinValue() <= VecEC.getKnownMinValue(),
+          "subvector operand of experimental_vector_insert would overrun the "
+          "vector being inserted into.");
+    }
     break;
   }
   case Intrinsic::experimental_vector_extract: {
     Value *Vec = Call.getArgOperand(0);
     Value *Idx = Call.getArgOperand(1);
     unsigned IdxN = cast<ConstantInt>(Idx)->getZExtValue();
+
     VectorType *ResultTy = cast<VectorType>(Call.getType());
     VectorType *VecTy = cast<VectorType>(Vec->getType());
 
+    ElementCount VecEC = VecTy->getElementCount();
+    ElementCount ResultEC = ResultTy->getElementCount();
+
     Assert(ResultTy->getElementType() == VecTy->getElementType(),
            "experimental_vector_extract result must have the same element "
            "type as the input vector.",
@@ -5336,6 +5352,13 @@
     Assert(IdxN % ResultTy->getElementCount().getKnownMinValue() == 0,
            "experimental_vector_extract index must be a constant multiple of "
            "the result type's known minimum vector length.");
+
+    // If this extraction is not the 'mixed' case where a fixed vector is is
+    // extracted from a scalable vector.
+    if (VecEC.isScalable() == ResultEC.isScalable()) {
+      Assert(IdxN + ResultEC.getKnownMinValue() <= VecEC.getKnownMinValue(),
+          "experimental_vector_extract would overrun.");
+    }
     break;
   }
   case Intrinsic::experimental_noalias_scope_decl: {
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -1863,12 +1863,6 @@
       unsigned SubVecNumElts = SubVecTy->getNumElements();
       unsigned IdxN = cast<ConstantInt>(Idx)->getZExtValue();
 
-      // The result of this call is undefined if the insertion overruns Vec.
-      if (IdxN + SubVecNumElts > VecNumElts) {
-        replaceInstUsesWith(CI, UndefValue::get(CI.getType()));
-        return eraseInstFromFunction(CI);
-      }
-
       // An insert that entirely overwrites Vec with SubVec is a nop.
       if (VecNumElts == SubVecNumElts) {
         replaceInstUsesWith(CI, SubVec);
@@ -1916,12 +1910,6 @@
       unsigned VecNumElts = VecTy->getNumElements();
       unsigned IdxN = cast<ConstantInt>(Idx)->getZExtValue();
 
-      // The result of this call is undefined if the extraction overruns Vec.
-      if (IdxN + DstNumElts > VecNumElts) {
-        replaceInstUsesWith(CI, UndefValue::get(CI.getType()));
-        return eraseInstFromFunction(CI);
-      }
-
       // Extracting the entirety of Vec is a nop.
       if (VecNumElts == DstNumElts) {
         replaceInstUsesWith(CI, Vec);
diff --git a/llvm/test/Verifier/insert-extract-intrinsics-invalid.ll b/llvm/test/Verifier/insert-extract-intrinsics-invalid.ll
--- a/llvm/test/Verifier/insert-extract-intrinsics-invalid.ll
+++ b/llvm/test/Verifier/insert-extract-intrinsics-invalid.ll
@@ -1,5 +1,9 @@
 ; RUN: not opt -verify -S < %s 2>&1 >/dev/null | FileCheck %s
 
+;
+; Test that extractions/insertion indices are validated.
+;
+
 ; CHECK: experimental_vector_extract index must be a constant multiple of the result type's known minimum vector length.
 define <4 x i32> @extract_idx_not_constant_multiple(<8 x i32> %vec) {
   %1 = call <4 x i32> @llvm.experimental.vector.extract.v4i32.v8i32(<8 x i32> %vec, i64 1)
@@ -12,5 +16,57 @@
   ret <8 x i32> %1
 }
 
+;
+; Test that extractions/insertions which 'overrun' are captured.
+;
+
+; CHECK: experimental_vector_extract would overrun.
+define <3 x i32> @extract_overrun_fixed_fixed(<8 x i32> %vec) {
+  %1 = call <3 x i32> @llvm.experimental.vector.extract.v8i32.v3i32(<8 x i32> %vec, i64 6)
+  ret <3 x i32> %1
+}
+
+; CHECK: experimental_vector_extract would overrun.
+define <vscale x 3 x i32> @extract_overrun_scalable_scalable(<vscale x 8 x i32> %vec) {
+  %1 = call <vscale x 3 x i32> @llvm.experimental.vector.extract.nxv8i32.nxv3i32(<vscale x 8 x i32> %vec, i64 6)
+  ret <vscale x 3 x i32> %1
+}
+
+; We cannot statically check whether or not an extraction of a fixed vector
+; from a scalable vector would overrun, because we can't compare the sizes of
+; the two. Therefore, this function should not raise verifier errors.
+; CHECK-NOT: experimental_vector_extract would overrun.
+define <3 x i32> @extract_overrun_scalable_fixed(<vscale x 8 x i32> %vec) {
+  %1 = call <3 x i32> @llvm.experimental.vector.extract.nxv8i32.v3i32(<vscale x 8 x i32> %vec, i64 6)
+  ret <3 x i32> %1
+}
+
+; CHECK: subvector operand of experimental_vector_insert would overrun the vector being inserted into.
+define <8 x i32> @insert_overrun_fixed_fixed(<8 x i32> %vec, <3 x i32> %subvec) {
+  %1 = call <8 x i32> @llvm.experimental.vector.insert.v8i32.v3i32(<8 x i32> %vec, <3 x i32> %subvec, i64 6)
+  ret <8 x i32> %1
+}
+
+; CHECK: subvector operand of experimental_vector_insert would overrun the vector being inserted into.
+define <vscale x 8 x i32> @insert_overrun_scalable_scalable(<vscale x 8 x i32> %vec, <vscale x 3 x i32> %subvec) {
+  %1 = call <vscale x 8 x i32> @llvm.experimental.vector.insert.nxv8i32.nxv3i32(<vscale x 8 x i32> %vec, <vscale x 3 x i32> %subvec, i64 6)
+  ret <vscale x 8 x i32> %1
+}
+
+; We cannot statically check whether or not an insertion of a fixed vector into
+; a scalable vector would overrun, because we can't compare the sizes of the
+; two. Therefore, this function should not raise verifier errors.
+; CHECK-NOT: subvector operand of experimental_vector_insert would overrun the vector being inserted into.
+define <vscale x 8 x i32> @insert_overrun_scalable_fixed(<vscale x 8 x i32> %vec, <3 x i32> %subvec) {
+  %1 = call <vscale x 8 x i32> @llvm.experimental.vector.insert.nxv8i32.v3i32(<vscale x 8 x i32> %vec, <3 x i32> %subvec, i64 6)
+  ret <vscale x 8 x i32> %1
+}
+
+declare <vscale x 3 x i32> @llvm.experimental.vector.extract.nxv8i32.nxv3i32(<vscale x 8 x i32>, i64)
+declare <vscale x 8 x i32> @llvm.experimental.vector.insert.nxv8i32.nxv3i32(<vscale x 8 x i32>, <vscale x 3 x i32>, i64)
+declare <vscale x 8 x i32> @llvm.experimental.vector.insert.nxv8i32.v3i32(<vscale x 8 x i32>, <3 x i32>, i64)
+declare <3 x i32> @llvm.experimental.vector.extract.nxv8i32.v3i32(<vscale x 8 x i32>, i64)
+declare <3 x i32> @llvm.experimental.vector.extract.v8i32.v3i32(<8 x i32>, i64)
 declare <4 x i32> @llvm.experimental.vector.extract.v4i32.v8i32(<8 x i32>, i64)
+declare <8 x i32> @llvm.experimental.vector.insert.v8i32.v3i32(<8 x i32>, <3 x i32>, i64)
 declare <8 x i32> @llvm.experimental.vector.insert.v8i32.v4i32(<8 x i32>, <4 x i32>, i64)