diff --git a/src/mesa/state_tracker/st_glsl_to_nir.cpp b/src/mesa/state_tracker/st_glsl_to_nir.cpp
index b989ad8c0b3..020d0d25322 100644
--- a/src/mesa/state_tracker/st_glsl_to_nir.cpp
+++ b/src/mesa/state_tracker/st_glsl_to_nir.cpp
@@ -69,6 +69,9 @@ st_nir_fixup_varying_slots(struct st_context *st, nir_shader *shader,
    if (st->needs_texcoord_semantic)
       return;
 
+   /* This is called from finalize, but we don't want to do this adjustment twice. */
+   assert(!st->allow_st_finalize_nir_twice);
+
    nir_foreach_variable_with_modes(var, shader, mode) {
       if (var->data.location >= VARYING_SLOT_VAR0) {
          var->data.location += 9;