diff --git a/src/axi_id_serialize.sv b/src/axi_id_serialize.sv
index b3d28e839..fc36a217f 100644
--- a/src/axi_id_serialize.sv
+++ b/src/axi_id_serialize.sv
@@ -55,7 +55,17 @@ module axi_id_serialize #(
   /// Request struct type of the AXI4+ATOP master port
   parameter type mst_req_t = logic,
   /// Response struct type of the AXI4+ATOP master port
-  parameter type mst_resp_t = logic
+  parameter type mst_resp_t = logic,
+  /// A custom offset (modulo `AxiMstPortMaxUniqIds`, ignored for input IDs remapped through
+  /// `IdMap`) for the assigned output IDs.
+  parameter int unsigned MstIdBaseOffset = 32'd0,
+  /// Explicit input-output ID map. If an input ID `id` does not appear in this mapping (default),
+  /// it is simply mapped to the output ID `id % AxiMstPortMaxUniqIds`. If `id` appears in more
+  /// than one entry, it is matched to the *last* matching entry's output ID.
+  /// Number of Entries in the explicit ID map (default: None)
+  parameter int unsigned IdMapNumEntries = 32'd0,
+  /// Explicit ID map; index [0] in each entry is the input ID to match, index [1] the output ID.
+  parameter int unsigned IdMap [IdMapNumEntries-1:0][0:1] = '{default: '{32'b0, 32'b0}}
 ) (
   /// Rising-edge clock of both ports
   input  logic      clk_i,
@@ -143,9 +153,27 @@ module axi_id_serialize #(
   /// R channel at master port
   `AXI_TYPEDEF_R_CHAN_T(mst_r_t, data_t, mst_id_t, user_t)
 
+  /// Type for slave ID map
+  typedef mst_id_t [2**AxiSlvPortIdWidth-1:0] slv_id_map_t;
+
+  /// Resolve target output ID for each possible input ID as a parameter
+  function automatic slv_id_map_t map_slv_ids();
+    slv_id_map_t ret = '0;
+    // Populate output with default mapping, including `MstIdBaseOffset`
+    for (int unsigned i = 0; i < 2**AxiSlvPortIdWidth; ++i)
+      ret[i] = (i + MstIdBaseOffset) % AxiMstPortMaxUniqIds;
+    // For each explicitly mapped input ID, set the desired output ID
+    for (int unsigned i = 0; i < IdMapNumEntries; ++i)
+      ret[IdMap[i][0]] = IdMap[i][1];
+    return ret;
+  endfunction
+
+  /// Input-to-output ID map used
+  localparam slv_id_map_t SlvIdMap = map_slv_ids();
+
   select_t slv_aw_select, slv_ar_select;
-  assign slv_aw_select = select_t'(slv_req_i.aw.id % AxiMstPortMaxUniqIds); // TODO: customizable base
-  assign slv_ar_select = select_t'(slv_req_i.ar.id % AxiMstPortMaxUniqIds);
+  assign slv_aw_select = select_t'(SlvIdMap[slv_req_i.aw.id]);
+  assign slv_ar_select = select_t'(SlvIdMap[slv_req_i.ar.id]);
 
   slv_req_t  [AxiMstPortMaxUniqIds-1:0] to_serializer_reqs;
   slv_resp_t [AxiMstPortMaxUniqIds-1:0] to_serializer_resps;