diff --git a/ice40/family.cmake b/ice40/family.cmake
index 1ed2ecf3..532d7cc4 100644
--- a/ice40/family.cmake
+++ b/ice40/family.cmake
@@ -17,7 +17,7 @@ foreach (dev ${devices})
     set(DEV_TXT_DB /usr/local/share/icebox/chipdb-${dev}.txt)
     set(DEV_CC_DB ${CMAKE_CURRENT_SOURCE_DIR}/ice40/chipdbs/chipdb-${dev}.cc)
     add_custom_command(OUTPUT ${DEV_CC_DB}
-            COMMAND python3 ${DB_PY} ${DEV_TXT_DB} > ${DEV_CC_DB}.new
+            COMMAND python3 ${DB_PY} -c ${DEV_TXT_DB} > ${DEV_CC_DB}.new
             COMMAND mv ${DEV_CC_DB}.new ${DEV_CC_DB}
             DEPENDS ${DEV_TXT_DB} ${DB_PY}
             )