diff --git a/llvm/test/Reduce/remove-bbs-ret-nonvoid.ll b/llvm/test/Reduce/remove-bbs-ret-nonvoid.ll
--- a/llvm/test/Reduce/remove-bbs-ret-nonvoid.ll
+++ b/llvm/test/Reduce/remove-bbs-ret-nonvoid.ll
@@ -13,10 +13,7 @@
 ; CHECK-NEXT:    br label %interesting2
 
 ; CHECK-LABEL: interesting2:
-; CHECK-NEXT:    br label %uninteresting1
-
-; CHECK-LABEL: uninteresting1:
-; CHECK-NEXT:    ret i32 10
+; CHECK-NEXT:    ret i32 undef
 
 interesting:
   br label %interesting2
diff --git a/llvm/tools/llvm-reduce/deltas/ReduceBasicBlocks.cpp b/llvm/tools/llvm-reduce/deltas/ReduceBasicBlocks.cpp
--- a/llvm/tools/llvm-reduce/deltas/ReduceBasicBlocks.cpp
+++ b/llvm/tools/llvm-reduce/deltas/ReduceBasicBlocks.cpp
@@ -45,7 +45,10 @@
   Term->eraseFromParent();
 
   if (ChunkSucessors.empty()) {
-    ReturnInst::Create(BB.getContext(), nullptr, &BB);
+    auto *FnRetTy = BB.getParent()->getReturnType();
+    ReturnInst::Create(BB.getContext(),
+                       FnRetTy->isVoidTy() ? nullptr : UndefValue::get(FnRetTy),
+                       &BB);
     return;
   }
 
@@ -66,7 +69,10 @@
 static void removeUninterestingBBsFromSwitch(SwitchInst &SwInst,
                                              std::set<BasicBlock *> BBsToKeep) {
   if (!BBsToKeep.count(SwInst.getDefaultDest())) {
-    ReturnInst::Create(SwInst.getContext(), nullptr, SwInst.getParent());
+    auto *FnRetTy = SwInst.getParent()->getParent()->getReturnType();
+    ReturnInst::Create(SwInst.getContext(),
+                       FnRetTy->isVoidTy() ? nullptr : UndefValue::get(FnRetTy),
+                       SwInst.getParent());
     SwInst.eraseFromParent();
   } else
     for (int I = 0, E = SwInst.getNumCases(); I != E; ++I) {