diff --git a/compiler/utils/arm/assembler_arm_vixl.h b/compiler/utils/arm/assembler_arm_vixl.h
index e81e767..66b22ea 100644
--- a/compiler/utils/arm/assembler_arm_vixl.h
+++ b/compiler/utils/arm/assembler_arm_vixl.h
@@ -241,6 +241,8 @@
 
 // Thread register declaration.
 extern const vixl32::Register tr;
+// Marking register declaration.
+extern const vixl32::Register mr;
 
 }  // namespace arm
 }  // namespace art