diff --git a/lldb/source/Plugins/Process/Utility/RegisterContextDarwin_arm64.cpp b/lldb/source/Plugins/Process/Utility/RegisterContextDarwin_arm64.cpp
index 308cf1519094..0f9e1e6b758b 100644
--- a/lldb/source/Plugins/Process/Utility/RegisterContextDarwin_arm64.cpp
+++ b/lldb/source/Plugins/Process/Utility/RegisterContextDarwin_arm64.cpp
@@ -429,7 +429,7 @@ bool RegisterContextDarwin_arm64::ReadRegister(const RegisterInfo *reg_info,
   case fpu_v29:
   case fpu_v30:
   case fpu_v31:
-    value.SetBytes(fpu.v[reg].bytes.buffer, reg_info->byte_size,
+    value.SetBytes(fpu.v[reg - fpu_v0].bytes.buffer, reg_info->byte_size,
                    endian::InlHostByteOrder());
     break;
 
@@ -621,7 +621,8 @@ bool RegisterContextDarwin_arm64::WriteRegister(const RegisterInfo *reg_info,
   case fpu_v29:
   case fpu_v30:
   case fpu_v31:
-    ::memcpy(fpu.v[reg].bytes.buffer, value.GetBytes(), value.GetByteSize());
+    ::memcpy(fpu.v[reg - fpu_v0].bytes.buffer, value.GetBytes(),
+             value.GetByteSize());
     break;
 
   case fpu_fpsr: