diff --git a/lib/Target/ARM/ARMConstantPoolValue.h b/lib/Target/ARM/ARMConstantPoolValue.h
index 6f4eddf7361..3119b54563d 100644
--- a/lib/Target/ARM/ARMConstantPoolValue.h
+++ b/lib/Target/ARM/ARMConstantPoolValue.h
@@ -15,6 +15,7 @@
 #define LLVM_TARGET_ARM_CONSTANTPOOLVALUE_H
 
 #include "llvm/CodeGen/MachineConstantPool.h"
+#include <cstddef>
 
 namespace llvm {