diff --git a/src/arch/x86_64/CodeGen.zig b/src/arch/x86_64/CodeGen.zig
index 0a209b8807..66bf43fb29 100644
--- a/src/arch/x86_64/CodeGen.zig
+++ b/src/arch/x86_64/CodeGen.zig
@@ -2968,9 +2968,8 @@ fn genSetReg(self: *Self, ty: Type, reg: Register, mcv: MCValue) InnerError!void
             _ = try self.addInst(.{
                 .tag = .mov,
                 .ops = (Mir.Ops{
-                    .reg1 = reg,
+                    .reg1 = registerAlias(reg, @divExact(src_reg.size(), 8)),
                     .reg2 = src_reg,
-                    .flags = 0b11,
                 }).encode(),
                 .data = undefined,
             });
diff --git a/src/arch/x86_64/Emit.zig b/src/arch/x86_64/Emit.zig
index a8260fa5c2..10aff52813 100644
--- a/src/arch/x86_64/Emit.zig
+++ b/src/arch/x86_64/Emit.zig
@@ -1119,17 +1119,7 @@ fn mirMovImpl(
                 encoder.imm32(imm_op);
                 break :blk;
             }
-            // mov reg1, reg2
-            // RM
-            const opc: u8 = if (ops.reg1.size() == 8) 0x8a else 0x8b;
-            const encoder = try Encoder.init(code, 3);
-            encoder.rex(.{
-                .w = ops.reg1.size() == 64 and ops.reg2.size() == 64,
-                .r = ops.reg1.isExtended(),
-                .b = ops.reg2.isExtended(),
-            });
-            encoder.opcode_1byte(opc);
-            encoder.modRm_direct(ops.reg1.lowId(), ops.reg2.lowId());
+            return EmitResult.err(allocator, src_loc, "TODO unused variant: mov reg1, reg2, 0b11", .{});
         },
     }
     return EmitResult.ok();
diff --git a/src/arch/x86_64/Mir.zig b/src/arch/x86_64/Mir.zig
index fe94310639..e2cc3cab30 100644
--- a/src/arch/x86_64/Mir.zig
+++ b/src/arch/x86_64/Mir.zig
@@ -145,7 +145,7 @@ pub const Inst = struct {
         ///       0b10  [reg1 + imm32], reg2
         ///       0b10  [reg1 + 0], imm32
         ///       0b11  [reg1 + imm32], imm32
-        ///       0b11  reg1, reg2 (RM)
+        ///       0b11  AVAILABLE
         /// Notes:
         ///  * If reg2 is `none` then it means Data field `imm` is used as the immediate.
         ///  * When two imm32 values are required, Data field `payload` points at `ImmPair`.