diff --git a/js/src/jit/mips64/CodeGenerator-mips64.cpp b/js/src/jit/mips64/CodeGenerator-mips64.cpp
index 68943c93d4d5..1af0ea2d2f19 100644
--- a/js/src/jit/mips64/CodeGenerator-mips64.cpp
+++ b/js/src/jit/mips64/CodeGenerator-mips64.cpp
@@ -186,12 +186,16 @@ void CodeGenerator::visitCompareI64(LCompareI64* lir) {
   Register lhsReg = ToRegister64(lhs).reg;
   Register output = ToRegister(lir->output());
   Register rhsReg;
+  ScratchRegisterScope scratch(masm);
 
   if (IsConstant(rhs)) {
-    rhsReg = ScratchRegister;
+    rhsReg = scratch;
     masm.ma_li(rhsReg, ImmWord(ToInt64(rhs)));
-  } else {
+  } else if (rhs.value().isGeneralReg()) {
     rhsReg = ToRegister64(rhs).reg;
+  } else {
+    rhsReg = scratch;
+    masm.loadPtr(ToAddress(rhs.value()), rhsReg);
   }
 
   bool isSigned = mir->compareType() == MCompare::Compare_Int64;
@@ -208,12 +212,16 @@ void CodeGenerator::visitCompareI64AndBranch(LCompareI64AndBranch* lir) {
   const LInt64Allocation rhs = lir->getInt64Operand(LCompareI64::Rhs);
   Register lhsReg = ToRegister64(lhs).reg;
   Register rhsReg;
+  ScratchRegisterScope scratch(masm);
 
   if (IsConstant(rhs)) {
-    rhsReg = ScratchRegister;
+    rhsReg = scratch;
     masm.ma_li(rhsReg, ImmWord(ToInt64(rhs)));
-  } else {
+  } else if (rhs.value().isGeneralReg()) {
     rhsReg = ToRegister64(rhs).reg;
+  } else {
+    rhsReg = scratch;
+    masm.loadPtr(ToAddress(rhs.value()), rhsReg);
   }
 
   bool isSigned = mir->compareType() == MCompare::Compare_Int64;