diff --git a/lib/intcode/assembler.ex b/lib/intcode/assembler.ex
index 4acbf32..506eed3 100644
--- a/lib/intcode/assembler.ex
+++ b/lib/intcode/assembler.ex
@@ -47,7 +47,7 @@ defmodule Assembler do
   def test do
     File.read!("test/intcode/cmp8.asm")
     |> assemble()
-    |> Day5.run_cli()
+    |> Day9.run_cli()
   end
 
   def assemble(asm) do
@@ -190,6 +190,11 @@ defmodule Assembler do
     [dest, b, a, 8 + modes | memory]
   end
 
+  def assemble_insn(["srel", val], memory) do
+    {[val], modes} = parse_params([val], [:read])
+    [val, 9 + modes | memory]
+  end
+
   def assemble_insn(["hlt"], memory) do
     [99 | memory]
   end
@@ -281,7 +286,7 @@ defmodule Assembler do
     |> Enum.with_index()
     |> Enum.map_reduce(0, fn {{param, type}, index}, modes ->
       val =
-        case Regex.run(~r/^\$?(\d+)$/, param) do
+        case Regex.run(~r/^[\$#]?(\d+)$/, param) do
           [_, digits] ->
             String.to_integer(digits)
 
@@ -290,6 +295,9 @@ defmodule Assembler do
               "$" <> param ->
                 {:expr, parse_param_expr(param)}
 
+              "#" <> param ->
+                {:expr, parse_param_expr(param)}
+
               _ ->
                 {:expr, parse_param_expr(param)}
             end
@@ -298,14 +306,25 @@ defmodule Assembler do
       modes =
         case type do
           :read ->
-            if String.starts_with?(param, "$") do
-              modes
-            else
-              modes + pow(10, index + 2)
+            cond do
+              String.starts_with?(param, "$") ->
+                modes
+
+              String.starts_with?(param, "#") ->
+                modes + 2 * pow(10, index + 2)
+
+              true ->
+                modes + pow(10, index + 2)
             end
 
-          _ ->
-            modes
+          :write ->
+            cond do
+              String.starts_with?(param, "#") ->
+                modes + 2 * pow(10, index + 2)
+
+              true ->
+                modes
+            end
         end
 
       {val, modes}
diff --git a/test/intcode/assembler_test.exs b/test/intcode/assembler_test.exs
index 1bd3005..ff51c20 100644
--- a/test/intcode/assembler_test.exs
+++ b/test/intcode/assembler_test.exs
@@ -21,6 +21,7 @@ defmodule AssemblerTest do
     assert assemble("clt $1, $2, $3") == [7, 1, 2, 3]
     assert assemble("ceq 1, 2, 3") == [1108, 1, 2, 3]
     assert assemble("ceq $1, $2, $3") == [8, 1, 2, 3]
+    assert assemble("srel 1234") == [109, 1234]
     assert assemble("hlt") == [99]
   end
 
@@ -140,4 +141,9 @@ defmodule AssemblerTest do
            label: 42
            """) == [101, 1, 6, 3, 42]
   end
+
+  test "assembles relative mode parameters" do
+    assert assemble("add #1, #2, #3") == [22201, 1, 2, 3]
+    assert assemble("in #4") == [203, 4]
+  end
 end