diff --git a/src/panfrost/bifrost/gen_pack.py b/src/panfrost/bifrost/gen_pack.py
index e8ccf9ea12d..e9025ae3fbc 100644
--- a/src/panfrost/bifrost/gen_pack.py
+++ b/src/panfrost/bifrost/gen_pack.py
@@ -181,10 +181,16 @@ def pack_register_format(mod, opts, body, pack_exprs):
     body.append('unsigned {}_temp = 0;'.format(mod))
 
     first = True
+    auto = None
     for i, op in enumerate(opts):
         if op is None or op == 'reserved':
             continue
 
+        if op == 'auto':
+            assert(auto == None)
+            auto = i
+            continue
+
         t_else = 'else ' if not first else ''
         first = False
         nir_type = REGISTER_FORMATS.get(op)
@@ -193,7 +199,10 @@ def pack_register_format(mod, opts, body, pack_exprs):
             body.append('{}if (ins->format == {}) {}_temp = {};'.format(t_else, nir_type, mod, i))
 
     assert not first
-    body.append('else unreachable("Could not pattern match register format");')
+    if auto is None:
+        body.append('else unreachable("Could not pattern match register format");')
+    else:
+        body.append('else {}_temp = {};'.format(mod, auto))
     return mod + '_temp'
 
 def pack_seg(mod, opts, body, pack_exprs):