diff --git a/llvm/lib/Target/Mips/MipsTargetMachine.cpp b/llvm/lib/Target/Mips/MipsTargetMachine.cpp
index 06f78e0..5046c1b 100644
--- a/llvm/lib/Target/Mips/MipsTargetMachine.cpp
+++ b/llvm/lib/Target/Mips/MipsTargetMachine.cpp
@@ -135,7 +135,13 @@
 class MipsPassConfig : public TargetPassConfig {
 public:
   MipsPassConfig(MipsTargetMachine *TM, PassManagerBase &PM)
-    : TargetPassConfig(TM, PM) {}
+    : TargetPassConfig(TM, PM) {
+    // The current implementation of long branch pass requires a scratch
+    // register ($at) to be available before branch instructions. Tail merging
+    // can break this requirement, so disable it when long branch pass is
+    // enabled.
+    EnableTailMerge = !getMipsSubtarget().enableLongBranchPass();
+  }
 
   MipsTargetMachine &getMipsTargetMachine() const {
     return getTM<MipsTargetMachine>();