diff --git a/ROMFS/px4fmu_common/init.d-posix/rcS b/ROMFS/px4fmu_common/init.d-posix/rcS
index eb13dc938a..e460c4019f 100644
--- a/ROMFS/px4fmu_common/init.d-posix/rcS
+++ b/ROMFS/px4fmu_common/init.d-posix/rcS
@@ -3,7 +3,7 @@
 # PX4 commands need the 'px4-' prefix in bash.
 # (px4-alias.sh is expected to be in the PATH)
 # shellcheck disable=SC1091
-source px4-alias.sh
+. px4-alias.sh
 
 SCRIPT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"