diff --git a/src/hotspot/cpu/x86/assembler_x86.cpp b/src/hotspot/cpu/x86/assembler_x86.cpp
index 67ff8a97c7a..1748a9fb06f 100644
--- a/src/hotspot/cpu/x86/assembler_x86.cpp
+++ b/src/hotspot/cpu/x86/assembler_x86.cpp
@@ -1763,8 +1763,9 @@ void Assembler::cmpl_imm32(Address dst, int32_t imm32) {
 
 void Assembler::cmpw(Address dst, int imm16) {
   InstructionMark im(this);
-  assert(!dst.base_needs_rex() && !dst.index_needs_rex(), "no extended registers");
-  emit_int16(0x66, (unsigned char)0x81);
+  emit_int8(0x66);
+  prefix(dst);
+  emit_int8((unsigned char)0x81);
   emit_operand(rdi, dst, 2);
   emit_int16(imm16);
 }