diff --git a/compiler/optimizing/code_generator_arm64.cc b/compiler/optimizing/code_generator_arm64.cc
index d56f7aa..5bca93f 100644
--- a/compiler/optimizing/code_generator_arm64.cc
+++ b/compiler/optimizing/code_generator_arm64.cc
@@ -1205,6 +1205,7 @@
   //      mr        : Runtime reserved.
   //      ip1       : VIXL core temp.
   //      ip0       : VIXL core temp.
+  //      x18       : Platform register.
   //
   // Blocked fp registers:
   //      d31       : VIXL fp temp.
@@ -1213,6 +1214,7 @@
   while (!reserved_core_registers.IsEmpty()) {
     blocked_core_registers_[reserved_core_registers.PopLowestIndex().GetCode()] = true;
   }
+  blocked_core_registers_[X18] = true;
 
   CPURegList reserved_fp_registers = vixl_reserved_fp_registers;
   while (!reserved_fp_registers.IsEmpty()) {