diff --git a/rules/preprocessing.smk b/rules/preprocessing.smk
index d5a4eb68..398a79a3 100644
--- a/rules/preprocessing.smk
+++ b/rules/preprocessing.smk
@@ -41,7 +41,7 @@ rule download_phone_data:
 rule download_fitbit_data:
     input:
         participant_file = "data/external/participant_files/{pid}.yaml",
-        input_file = "" if config["SENSOR_DATA"]["FITBIT"]["SOURCE"]["TYPE"] == "DATABASE" else lambda wildcards: config["FITBIT_" + str(wildcards.sensor).upper()]["TABLE"]["CSV"][str(wildcards.fitbit_data_type).upper()] 
+        input_file = [] if config["SENSOR_DATA"]["FITBIT"]["SOURCE"]["TYPE"] == "DATABASE" else lambda wildcards: config["FITBIT_" + str(wildcards.sensor).upper()]["TABLE"]["CSV"][str(wildcards.fitbit_data_type).upper()] 
     params:
         source = config["SENSOR_DATA"]["FITBIT"]["SOURCE"],
         sensor = "fitbit_" + "{sensor}",