diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -4896,9 +4896,9 @@
       any_of(Indices, [](const auto *V) { return isa<PoisonValue>(V); }))
     return PoisonValue::get(GEPTy);
 
+  // getelementptr undef, idx -> undef
   if (Q.isUndefValue(Ptr))
-    // If inbounds, we can choose an out-of-bounds pointer as a base pointer.
-    return InBounds ? PoisonValue::get(GEPTy) : UndefValue::get(GEPTy);
+    return UndefValue::get(GEPTy);
 
   bool IsScalableVec =
       isa<ScalableVectorType>(SrcTy) || any_of(Indices, [](const Value *V) {
diff --git a/llvm/test/Transforms/InstSimplify/gep.ll b/llvm/test/Transforms/InstSimplify/gep.ll
--- a/llvm/test/Transforms/InstSimplify/gep.ll
+++ b/llvm/test/Transforms/InstSimplify/gep.ll
@@ -160,7 +160,7 @@
 
 define ptr @undef_inbounds_var_idx(i64 %idx) {
 ; CHECK-LABEL: @undef_inbounds_var_idx(
-; CHECK-NEXT:    ret ptr poison
+; CHECK-NEXT:    ret ptr undef
 ;
   %el = getelementptr inbounds i64, ptr undef, i64 %idx
   ret ptr %el
@@ -176,7 +176,7 @@
 
 define <8 x ptr> @undef_vec1() {
 ; CHECK-LABEL: @undef_vec1(
-; CHECK-NEXT:    ret <8 x ptr> poison
+; CHECK-NEXT:    ret <8 x ptr> undef
 ;
   %el = getelementptr inbounds i64, ptr undef, <8 x i64> undef
   ret <8 x ptr> %el