diff --git a/llvm/lib/Target/SystemZ/SystemZLongBranch.cpp b/llvm/lib/Target/SystemZ/SystemZLongBranch.cpp
index f19b932f3c731..8103bfe5f4f12 100644
--- a/llvm/lib/Target/SystemZ/SystemZLongBranch.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZLongBranch.cpp
@@ -218,6 +218,7 @@ static unsigned getInstSizeInBytes(const MachineInstr &MI,
           // These do not have a size:
           MI.isDebugOrPseudoInstr() || MI.isPosition() || MI.isKill() ||
           MI.isImplicitDef() || MI.getOpcode() == TargetOpcode::MEMBARRIER ||
+          MI.getOpcode() == TargetOpcode::INIT_UNDEF ||
           // These have a size that may be zero:
           MI.isInlineAsm() || MI.getOpcode() == SystemZ::STACKMAP ||
           MI.getOpcode() == SystemZ::PATCHPOINT ||
diff --git a/llvm/test/CodeGen/SystemZ/init-undef.mir b/llvm/test/CodeGen/SystemZ/init-undef.mir
new file mode 100644
index 0000000000000..101dc6ebf8fd5
--- /dev/null
+++ b/llvm/test/CodeGen/SystemZ/init-undef.mir
@@ -0,0 +1,17 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 5
+# REQUIRES: asserts
+# RUN: llc -run-pass systemz-long-branch -mtriple=s390x-ibm-zos -o - %s | FileCheck %s
+
+# Makes sure INIT_UNDEF does not crash the compiler in systemz-long-branch
+---
+name: func0
+body: |
+  bb.0.entry:
+    ; CHECK-LABEL: name: func0
+    ; CHECK: renamable $r0l = INIT_UNDEF
+    ; CHECK-NEXT: renamable $r3d = LGFR killed renamable $r0l
+    ; CHECK-NEXT: frame-destroy Return_XPLINK implicit $r3d
+    renamable $r0l = INIT_UNDEF
+    renamable $r3d = LGFR killed renamable $r0l
+    frame-destroy Return_XPLINK implicit $r3d
+...