diff --git a/py/mkrules.cmake b/py/mkrules.cmake
index 743302aea..bfc56abfe 100644
--- a/py/mkrules.cmake
+++ b/py/mkrules.cmake
@@ -99,6 +99,7 @@ add_custom_command(
 add_custom_command(
     OUTPUT ${MICROPY_QSTRDEFS_COLLECTED}
     COMMAND ${Python3_EXECUTABLE} ${MICROPY_PY_DIR}/makeqstrdefs.py cat qstr _ ${MICROPY_GENHDR_DIR}/qstr ${MICROPY_QSTRDEFS_COLLECTED}
+    BYPRODUCTS "${MICROPY_QSTRDEFS_COLLECTED}.hash"
     DEPENDS ${MICROPY_QSTRDEFS_SPLIT}
     VERBATIM
     COMMAND_EXPAND_LISTS
@@ -136,6 +137,7 @@ add_custom_command(
 add_custom_command(
     OUTPUT ${MICROPY_MODULEDEFS_COLLECTED}
     COMMAND ${Python3_EXECUTABLE} ${MICROPY_PY_DIR}/makeqstrdefs.py cat module _ ${MICROPY_GENHDR_DIR}/module ${MICROPY_MODULEDEFS_COLLECTED}
+    BYPRODUCTS "${MICROPY_MODULEDEFS_COLLECTED}.hash"
     DEPENDS ${MICROPY_MODULEDEFS_SPLIT}
     VERBATIM
     COMMAND_EXPAND_LISTS
@@ -161,6 +163,7 @@ add_custom_command(
 add_custom_command(
     OUTPUT ${MICROPY_ROOT_POINTERS_COLLECTED}
     COMMAND ${Python3_EXECUTABLE} ${MICROPY_PY_DIR}/makeqstrdefs.py cat root_pointer _ ${MICROPY_GENHDR_DIR}/root_pointer ${MICROPY_ROOT_POINTERS_COLLECTED}
+    BYPRODUCTS "${MICROPY_ROOT_POINTERS_COLLECTED}.hash"
     DEPENDS ${MICROPY_ROOT_POINTERS_SPLIT}
     VERBATIM
     COMMAND_EXPAND_LISTS