diff --git a/reference/micropython/rp2/__init__.pyi b/reference/micropython/rp2/__init__.pyi
index 91af11f9b..aa1e8b688 100644
--- a/reference/micropython/rp2/__init__.pyi
+++ b/reference/micropython/rp2/__init__.pyi
@@ -40,6 +40,7 @@ def asm_pio(
     out_init: Union[Pin, List[Pin], int, List[int], None] = None,
     set_init: Union[Pin, List[Pin], int, List[int], None] = None,
     sideset_init: Union[Pin, List[Pin], int, List[int], None] = None,
+    side_pindir: bool = False,
     in_shiftdir=0,
     out_shiftdir=0,
     autopush=False,
@@ -59,8 +60,10 @@ def asm_pio(
     - *out_init* configures the pins used for ``out()`` instructions.
     - *set_init* configures the pins used for ``set()`` instructions. There can
       be at most 5.
-    - *sideset_init* configures the pins used side-setting. There can be at
-      most 5.
+    - *sideset_init* configures the pins used for ``.side()`` modifiers. There
+      can be at most 5.
+    - *side_pindir* when set to ``True`` configures ``.side()`` modifiers to be
+      used for pin directions, instead of pin values (the default, when ``False``).
 
     The following parameters are used by default, but can be overridden in
     `StateMachine.init()`: