diff --git a/CodeGenA64/regs.h b/CodeGenA64/regs.h
index 4c5ac51e..244fc895 100644
--- a/CodeGenA64/regs.h
+++ b/CodeGenA64/regs.h
@@ -37,7 +37,7 @@ extern std::array<base::CpuReg, 32> FLT_REGS;
 
 extern base::CpuReg GPR_HELPER_REG;
 
-const constexpr uint32_t GPR_REGS_MASK = 0x7fffffff;
+const constexpr uint32_t GPR_REGS_MASK = 0x7ffeffff;
 const constexpr uint32_t GPR_LAC_REGS_MASK = 0x3ffe0000;
 const constexpr uint32_t GPR_LAC_REGS_MASK_WITH_LR = 0x7ffe0000;
 const constexpr uint32_t FLT_REGS_MASK = 0xffffffff;
diff --git a/CodeGenA64/regs.py b/CodeGenA64/regs.py
index fb273753..e3bf5d4a 100644
--- a/CodeGenA64/regs.py
+++ b/CodeGenA64/regs.py
@@ -72,7 +72,8 @@ def MaskToFlt64Regs(mask: int) -> List[ir.CpuReg]:
 # We do not really care about the 32 vs 64 bit for these
 _LINK_REG_MASK = 1 << 30
 
-GPR_REGS_MASK = 0x7fffffff
+# excludes x16 which we have reserved
+GPR_REGS_MASK = 0x7ffeffff
 GPR_LAC_REGS_MASK = 0x3ffe0000
 GPR_LAC_REGS_MASK_WITH_LR = 0x7ffe0000
 GPR_SPECIAL_MASK = 0x00010000