diff --git a/Makefile.ac b/Makefile.ac
index 90e2b5e3d0..1886c829bc 100644
--- a/Makefile.ac
+++ b/Makefile.ac
@@ -64,11 +64,19 @@ Q=@
 #
 ifeq ($(MAKECMDGOALS),all_ac_h)
 -include $(MAKEFILE_AC)
-endif
 
 # telemetry periodic frequency defaults to 60Hz
 TELEMETRY_FREQUENCY ?= 60
 
+ifdef PERIODIC_FREQUENCY
+DEFAULT_MODULES_FREQUENCY = $(PERIODIC_FREQUENCY)
+else
+$(error Error: PERIODIC_FREQUENCY not configured)
+endif
+
+endif
+
+
 init:
 	@[ -d $(PAPARAZZI_HOME) ] || (echo "Copying config example in your $(PAPARAZZI_HOME) directory"; mkdir -p $(PAPARAZZI_HOME); cp -a conf $(PAPARAZZI_HOME); cp -a data $(PAPARAZZI_HOME); mkdir -p $(PAPARAZZI_HOME)/var/maps; mkdir -p $(PAPARAZZI_HOME)/var/include)
 
@@ -147,7 +155,7 @@ $(MODULES_H) : $(CONF)/$(AIRFRAME_XML) $(TOOLS)/gen_modules.out $(CONF)/modules/
 	$(Q)test -d $(AC_GENERATED) || mkdir -p $(AC_GENERATED)
 	@echo GENERATE $@
 	$(eval $@_TMP := $(shell $(MKTEMP)))
-	$(Q)$(TOOLS)/gen_modules.out $(SETTINGS_MODULES) $< > $($@_TMP)
+	$(Q)$(TOOLS)/gen_modules.out $(SETTINGS_MODULES) $(DEFAULT_MODULES_FREQUENCY) $< > $($@_TMP)
 	$(Q)mv $($@_TMP) $@
 	$(Q)chmod a+r $@
 
diff --git a/sw/tools/gen_modules.ml b/sw/tools/gen_modules.ml
index ddd39ea0ee..7a32fcfe1c 100644
--- a/sw/tools/gen_modules.ml
+++ b/sw/tools/gen_modules.ml
@@ -344,9 +344,10 @@ let write_settings = fun xml_file out_set modules ->
 let h_name = "MODULES_H"
 
 let () =
-  if Array.length Sys.argv <> 3 then
-    failwith (Printf.sprintf "Usage: %s out_settings_file xml_file" Sys.argv.(0));
-  let xml_file = Sys.argv.(2)
+  if Array.length Sys.argv <> 4 then
+    failwith (Printf.sprintf "Usage: %s out_settings_file default_freq xml_file" Sys.argv.(0));
+  let xml_file = Sys.argv.(3)
+  and default_freq = int_of_string(Sys.argv.(2))
   and out_set = open_out Sys.argv.(1) in
   try
     let xml = start_and_begin xml_file h_name in
@@ -357,7 +358,7 @@ let () =
     nl ();
     (* Extract main_freq parameter *)
     let modules = try (ExtXml.child xml "modules") with _ -> Xml.Element("modules",[],[]) in
-    let main_freq = try (int_of_string (Xml.attrib modules "main_freq")) with _ -> !freq in
+    let main_freq = try (int_of_string (Xml.attrib modules "main_freq")) with _ -> default_freq in
     freq := main_freq;
     fprintf out_h "#define MODULES_FREQUENCY %d\n" !freq;
     nl ();