diff --git a/src/lj_asm.c b/src/lj_asm.c
index d961927b..753fe6bd 100644
--- a/src/lj_asm.c
+++ b/src/lj_asm.c
@@ -2015,6 +2015,7 @@ static void asm_setup_regsp(ASMState *as)
     ir->prev = REGSP_INIT;
     if (irt_is64(ir->t) && ir->o != IR_KNULL) {
 #if LJ_GC64
+      /* The false-positive of irt_is64() for ASMREF_L (REF_NIL) is OK here. */
       ir->i = 0;  /* Will become non-zero only for RIP-relative addresses. */
 #else
       /* Make life easier for backends by putting address of constant in i. */
diff --git a/src/lj_ir.h b/src/lj_ir.h
index 34c27853..8057a750 100644
--- a/src/lj_ir.h
+++ b/src/lj_ir.h
@@ -377,10 +377,12 @@ typedef struct IRType1 { uint8_t irt; } IRType1;
 #define irt_isint64(t)		(irt_typerange((t), IRT_I64, IRT_U64))
 
 #if LJ_GC64
+/* Include IRT_NIL, so IR(ASMREF_L) (aka REF_NIL) is considered 64 bit. */
 #define IRT_IS64 \
   ((1u<<IRT_NUM)|(1u<<IRT_I64)|(1u<<IRT_U64)|(1u<<IRT_P64)|\
    (1u<<IRT_LIGHTUD)|(1u<<IRT_STR)|(1u<<IRT_THREAD)|(1u<<IRT_PROTO)|\
-   (1u<<IRT_FUNC)|(1u<<IRT_CDATA)|(1u<<IRT_TAB)|(1u<<IRT_UDATA))
+   (1u<<IRT_FUNC)|(1u<<IRT_CDATA)|(1u<<IRT_TAB)|(1u<<IRT_UDATA)|\
+   (1u<<IRT_NIL))
 #elif LJ_64
 #define IRT_IS64 \
   ((1u<<IRT_NUM)|(1u<<IRT_I64)|(1u<<IRT_U64)|(1u<<IRT_P64)|(1u<<IRT_LIGHTUD))
diff --git a/src/lj_opt_sink.c b/src/lj_opt_sink.c
index 929ccb61..a16d112f 100644
--- a/src/lj_opt_sink.c
+++ b/src/lj_opt_sink.c
@@ -219,6 +219,7 @@ static void sink_sweep_ins(jit_State *J)
   for (ir = IR(J->cur.nk); ir < irbase; ir++) {
     irt_clearmark(ir->t);
     ir->prev = REGSP_INIT;
+    /* The false-positive of irt_is64() for ASMREF_L (REF_NIL) is OK here. */
     if (irt_is64(ir->t) && ir->o != IR_KNULL)
       ir++;
   }