diff --git a/src/compiler/nir/nir_lower_bit_size.c b/src/compiler/nir/nir_lower_bit_size.c
index 6e7b26bff45..81bc4489d97 100644
--- a/src/compiler/nir/nir_lower_bit_size.c
+++ b/src/compiler/nir/nir_lower_bit_size.c
@@ -184,6 +184,31 @@ lower_intrinsic_instr(nir_builder *b, nir_intrinsic_instr *intrin,
    }
 }
 
+static void
+lower_phi_instr(nir_builder *b, nir_phi_instr *phi, unsigned bit_size,
+                nir_phi_instr *last_phi)
+{
+   assert(phi->dest.is_ssa);
+   unsigned old_bit_size = phi->dest.ssa.bit_size;
+   assert(old_bit_size < bit_size);
+
+   nir_foreach_phi_src(src, phi) {
+      b->cursor = nir_after_block_before_jump(src->pred);
+      assert(src->src.is_ssa);
+      nir_ssa_def *new_src = nir_u2u(b, src->src.ssa, bit_size);
+
+      nir_instr_rewrite_src(&phi->instr, &src->src, nir_src_for_ssa(new_src));
+   }
+
+   phi->dest.ssa.bit_size = bit_size;
+
+   b->cursor = nir_after_instr(&last_phi->instr);
+
+   nir_ssa_def *new_dest = nir_u2u(b, &phi->dest.ssa, old_bit_size);
+   nir_ssa_def_rewrite_uses_after(&phi->dest.ssa, nir_src_for_ssa(new_dest),
+                                  new_dest->parent_instr);
+}
+
 static bool
 lower_impl(nir_function_impl *impl,
            nir_lower_bit_size_callback callback,
@@ -194,6 +219,9 @@ lower_impl(nir_function_impl *impl,
    bool progress = false;
 
    nir_foreach_block(block, impl) {
+      /* Stash this so we can rewrite phi destinations quickly. */
+      nir_phi_instr *last_phi = nir_block_last_phi_instr(block);
+
       nir_foreach_instr_safe(instr, block) {
          unsigned lower_bit_size = callback(instr, callback_data);
          if (lower_bit_size == 0)
@@ -209,6 +237,11 @@ lower_impl(nir_function_impl *impl,
                                   lower_bit_size);
             break;
 
+         case nir_instr_type_phi:
+            lower_phi_instr(&b, nir_instr_as_phi(instr),
+                            lower_bit_size, last_phi);
+            break;
+
          default:
             unreachable("Unsupported instruction type");
          }