diff --git a/llvm/lib/Transforms/IPO/MergeFunctions.cpp b/llvm/lib/Transforms/IPO/MergeFunctions.cpp
index 1428a09040a34..591be6be092c6 100644
--- a/llvm/lib/Transforms/IPO/MergeFunctions.cpp
+++ b/llvm/lib/Transforms/IPO/MergeFunctions.cpp
@@ -747,6 +747,7 @@ void MergeFunctions::writeThunk(Function *F, Function *G) {
     NewG = Function::Create(G->getFunctionType(), G->getLinkage(),
                             G->getAddressSpace(), "", G->getParent());
     NewG->setComdat(G->getComdat());
+    NewG->IsNewDbgInfoFormat = G->IsNewDbgInfoFormat;
     BB = BasicBlock::Create(F->getContext(), "", NewG);
   }
 
@@ -874,6 +875,7 @@ void MergeFunctions::mergeTwoFunctions(Function *F, Function *G) {
                                       F->getAddressSpace(), "", F->getParent());
     NewF->copyAttributesFrom(F);
     NewF->takeName(F);
+    NewF->IsNewDbgInfoFormat = F->IsNewDbgInfoFormat;
     // Ensure CFI type metadata is propagated to the new function.
     copyMetadataIfPresent(F, NewF, "type");
     copyMetadataIfPresent(F, NewF, "kcfi_type");
diff --git a/llvm/test/Transforms/MergeFunc/debuginfo-iterators.ll b/llvm/test/Transforms/MergeFunc/debuginfo-iterators.ll
new file mode 100644
index 0000000000000..7f259159ce9d3
--- /dev/null
+++ b/llvm/test/Transforms/MergeFunc/debuginfo-iterators.ll
@@ -0,0 +1,54 @@
+;; Ensure that the MergeFunctions pass creates thunks with the appropriate debug
+;; info format set (which would otherwise assert when inlining those thunks).
+; RUN: opt -S -passes=mergefunc,inline --try-experimental-debuginfo-iterators < %s | FileCheck %s
+
+declare void @f1()
+declare void @f2()
+
+define void @f3() {
+  call void @f1()
+  call void @f2()
+  ret void
+}
+
+;; MergeFunctions will replace f4 with a thunk that calls f3. Inlining will
+;; inline f3 into that thunk, which would assert if the thunk had the incorrect
+;; debug info format.
+define void @f4() {
+  call void @f1()
+  call void @f2()
+  ret void
+}
+
+; CHECK-LABEL: define void @f4() {
+; CHECK-NEXT:    call void @f1()
+; CHECK-NEXT:    call void @f2()
+; CHECK-NEXT:    ret void
+; CHECK-NEXT: }
+
+;; Both of these are interposable, so MergeFunctions will create a common thunk
+;; that both will call. Inlining will inline that thunk back, which would assert
+;; if the thunk had the incorrect debug info format.
+define weak void @f5() {
+  call void @f2()
+  call void @f1()
+  ret void
+}
+
+define weak void @f6() {
+  call void @f2()
+  call void @f1()
+  ret void
+}
+
+; CHECK-LABEL: define weak void @f6() {
+; CHECK-NEXT:    call void @f2()
+; CHECK-NEXT:    call void @f1()
+; CHECK-NEXT:    ret void
+; CHECK-NEXT:  }
+
+; CHECK-LABEL: define weak void @f5() {
+; CHECK-NEXT:    call void @f2()
+; CHECK-NEXT:    call void @f1()
+; CHECK-NEXT:    ret void
+; CHECK-NEXT:  }