diff --git a/src/asahi/lib/shaders/tessellation.cl b/src/asahi/lib/shaders/tessellation.cl
index a5725af6d5a..1ad831460df 100644
--- a/src/asahi/lib/shaders/tessellation.cl
+++ b/src/asahi/lib/shaders/tessellation.cl
@@ -187,6 +187,25 @@ libagx_tess_setup_indirect(global struct libagx_tess_args *p, bool with_counts,
       /* TODO */
    }
 
+   global struct agx_ia_state *ia = p->ia;
+   ia->verts_per_instance = count;
+
+   /* If indexing is enabled, the third word is the offset into the index buffer
+    * in elements. Apply that offset now that we have it. For a hardware
+    * indirect draw, the hardware would do this for us, but for software input
+    * assembly we need to do it ourselves.
+    *
+    * XXX: Deduplicate?
+    */
+   if (p->in_index_size_B) {
+      ia->index_buffer =
+         libagx_index_buffer(p->in_index_buffer, p->in_index_buffer_range_el,
+                             p->indirect[2], p->in_index_size_B, 0);
+
+      ia->index_buffer_range_el = libagx_index_buffer_range_el(
+         p->in_index_buffer_range_el, p->indirect[2]);
+   }
+
    /* VS grid size */
    p->grids[0] = count;
    p->grids[1] = instance_count;
diff --git a/src/asahi/lib/shaders/tessellator.h b/src/asahi/lib/shaders/tessellator.h
index 4350a5573a2..c987fd277cf 100644
--- a/src/asahi/lib/shaders/tessellator.h
+++ b/src/asahi/lib/shaders/tessellator.h
@@ -81,6 +81,9 @@ struct libagx_tess_args {
     */
    GLOBAL(uint32_t) grids;
 
+   /* For indirect draws, the output input assembly descriptor */
+   GLOBAL(struct agx_ia_state) ia;
+
    /* For indirect draws, the indirect draw descriptor. */
    GLOBAL(uint32_t) indirect;
 
@@ -91,6 +94,11 @@ struct libagx_tess_args {
     */
    GLOBAL(uint64_t) vertex_output_buffer_ptr;
 
+   /* Yet more indirect draw garbage. I need a refactor. */
+   uint64_t in_index_buffer;
+   uint32_t in_index_buffer_range_el;
+   uint32_t in_index_size_B;
+
    /* When geom+tess used together, the buffer containing TES outputs (executed
     * as a hardware compute shader).
     */
@@ -126,4 +134,4 @@ struct libagx_tess_args {
    /* Number of patches being tessellated */
    uint32_t nr_patches;
 } PACKED;
-AGX_STATIC_ASSERT(sizeof(struct libagx_tess_args) == 42 * 4);
+AGX_STATIC_ASSERT(sizeof(struct libagx_tess_args) == 48 * 4);