diff --git a/js/src/jit/MacroAssembler.h b/js/src/jit/MacroAssembler.h
index ba3e6669ed1e..6f34a77f099f 100644
--- a/js/src/jit/MacroAssembler.h
+++ b/js/src/jit/MacroAssembler.h
@@ -780,9 +780,9 @@ class MacroAssembler : public MacroAssemblerSpecific
     inline void subPtr(ImmWord imm, Register dest) DEFINED_ON(x64);
     inline void subPtr(const Address& addr, Register dest) DEFINED_ON(mips_shared, arm, arm64, x86, x64);
 
-    inline void sub64(Register64 src, Register64 dest) DEFINED_ON(x86, x64, arm);
-    inline void sub64(Imm64 imm, Register64 dest) DEFINED_ON(x86, x64, arm);
-    inline void sub64(const Operand& src, Register64 dest) DEFINED_ON(x64);
+    inline void sub64(Register64 src, Register64 dest) DEFINED_ON(x86, x64, arm, mips64);
+    inline void sub64(Imm64 imm, Register64 dest) DEFINED_ON(x86, x64, arm, mips64);
+    inline void sub64(const Operand& src, Register64 dest) DEFINED_ON(x64, mips64);
 
     inline void subFloat32(FloatRegister src, FloatRegister dest) PER_SHARED_ARCH;
 
diff --git a/js/src/jit/mips-shared/CodeGenerator-mips-shared.cpp b/js/src/jit/mips-shared/CodeGenerator-mips-shared.cpp
index 9731b528ccca..60d877e35ba9 100644
--- a/js/src/jit/mips-shared/CodeGenerator-mips-shared.cpp
+++ b/js/src/jit/mips-shared/CodeGenerator-mips-shared.cpp
@@ -375,6 +375,22 @@ CodeGeneratorMIPSShared::visitSubI(LSubI* ins)
     bailoutFrom(&overflow, ins->snapshot());
 }
 
+void
+CodeGeneratorMIPSShared::visitSubI64(LSubI64* lir)
+{
+    const LInt64Allocation lhs = lir->getInt64Operand(LSubI64::Lhs);
+    const LInt64Allocation rhs = lir->getInt64Operand(LSubI64::Rhs);
+
+    MOZ_ASSERT(ToOutRegister64(lir) == ToRegister64(lhs));
+
+    if (IsConstant(rhs)) {
+        masm.sub64(Imm64(ToInt64(rhs)), ToRegister64(lhs));
+        return;
+    }
+
+    masm.sub64(ToOperandOrRegister64(rhs), ToRegister64(lhs));
+}
+
 void
 CodeGeneratorMIPSShared::visitMulI(LMulI* ins)
 {
diff --git a/js/src/jit/mips-shared/CodeGenerator-mips-shared.h b/js/src/jit/mips-shared/CodeGenerator-mips-shared.h
index 974b34aad2a0..e987d2d6c376 100644
--- a/js/src/jit/mips-shared/CodeGenerator-mips-shared.h
+++ b/js/src/jit/mips-shared/CodeGenerator-mips-shared.h
@@ -130,6 +130,7 @@ class CodeGeneratorMIPSShared : public CodeGeneratorShared
     virtual void visitAddI(LAddI* ins);
     virtual void visitAddI64(LAddI64* ins);
     virtual void visitSubI(LSubI* ins);
+    virtual void visitSubI64(LSubI64* ins);
     virtual void visitBitNotI(LBitNotI* ins);
     virtual void visitBitOpI(LBitOpI* ins);
     virtual void visitBitOpI64(LBitOpI64* ins);
diff --git a/js/src/jit/mips64/MacroAssembler-mips64-inl.h b/js/src/jit/mips64/MacroAssembler-mips64-inl.h
index e2d9746d6010..e7d4ba6cce1e 100644
--- a/js/src/jit/mips64/MacroAssembler-mips64-inl.h
+++ b/js/src/jit/mips64/MacroAssembler-mips64-inl.h
@@ -212,6 +212,33 @@ MacroAssembler::subPtr(Imm32 imm, Register dest)
     ma_dsubu(dest, dest, imm);
 }
 
+void
+MacroAssembler::sub64(Register64 src, Register64 dest)
+{
+    as_dsubu(dest.reg, dest.reg, src.reg);
+}
+
+void
+MacroAssembler::sub64(const Operand& src, Register64 dest)
+{
+    if (src.getTag() == Operand::MEM) {
+        Register64 scratch(ScratchRegister);
+
+        load64(src.toAddress(), scratch);
+        sub64(scratch, dest);
+    } else {
+        sub64(Register64(src.toReg()), dest);
+    }
+}
+
+void
+MacroAssembler::sub64(Imm64 imm, Register64 dest)
+{
+    MOZ_ASSERT(dest.reg != ScratchRegister);
+    mov(ImmWord(imm.value), ScratchRegister);
+    as_dsubu(dest.reg, dest.reg, ScratchRegister);
+}
+
 void
 MacroAssembler::mul64(Imm64 imm, const Register64& dest)
 {