diff --git a/libraries/AP_Module/AP_Module.cpp b/libraries/AP_Module/AP_Module.cpp
index 741a83b56a..f11eb637a9 100644
--- a/libraries/AP_Module/AP_Module.cpp
+++ b/libraries/AP_Module/AP_Module.cpp
@@ -235,7 +235,7 @@ void AP_Module::call_hook_gyro_sample(uint8_t instance, float dt, const Vector3f
 /*
   call any accel_sample hooks
 */
-void AP_Module::call_hook_accel_sample(uint8_t instance, float dt, const Vector3f &accel)
+void AP_Module::call_hook_accel_sample(uint8_t instance, float dt, const Vector3f &accel, bool fsync_set)
 {
 #if AP_MODULE_SUPPORTED
     if (hooks[HOOK_ACCEL_SAMPLE] == nullptr) {
@@ -254,6 +254,7 @@ void AP_Module::call_hook_accel_sample(uint8_t instance, float dt, const Vector3
     state.accel[0] = accel[0];
     state.accel[1] = accel[1];
     state.accel[2] = accel[2];
+    state.fsync_set = fsync_set;
 
     for (const struct hook_list *h=hooks[HOOK_ACCEL_SAMPLE]; h; h=h->next) {
         ap_hook_accel_sample_fn_t fn = reinterpret_cast<ap_hook_accel_sample_fn_t>(h->symbol);
diff --git a/libraries/AP_Module/AP_Module.h b/libraries/AP_Module/AP_Module.h
index 8cf5fb73e3..429abd6b52 100644
--- a/libraries/AP_Module/AP_Module.h
+++ b/libraries/AP_Module/AP_Module.h
@@ -60,7 +60,7 @@ public:
     static void call_hook_gyro_sample(uint8_t instance, float dt, const Vector3f &gyro);
 
     // call any accel_sample hooks
-    static void call_hook_accel_sample(uint8_t instance, float dt, const Vector3f &accel);
+    static void call_hook_accel_sample(uint8_t instance, float dt, const Vector3f &accel, bool fsync_set);
     
     
 private:
diff --git a/libraries/AP_Module/AP_Module_Structures.h b/libraries/AP_Module/AP_Module_Structures.h
index 8905a3af8f..5e820c31d2 100644
--- a/libraries/AP_Module/AP_Module_Structures.h
+++ b/libraries/AP_Module/AP_Module_Structures.h
@@ -17,7 +17,7 @@ extern "C" {
 
 #define AHRS_state_version 1
 #define gyro_sample_version 1
-#define accel_sample_version 1
+#define accel_sample_version 2
 
 enum AHRS_status {
     AHRS_STATUS_INITIALISING    = 0,
@@ -122,6 +122,9 @@ struct accel_sample {
 
     // body frame rates in m/s/s
     float accel[3];
+
+    // true if external frame sync is set
+    bool fsync_set;
 };
     
 /*
diff --git a/libraries/AP_Module/examples/ModuleTest/module/moduletest.c b/libraries/AP_Module/examples/ModuleTest/module/moduletest.c
index ca89074266..4d5c1b62cc 100644
--- a/libraries/AP_Module/examples/ModuleTest/module/moduletest.c
+++ b/libraries/AP_Module/examples/ModuleTest/module/moduletest.c
@@ -53,13 +53,21 @@ void ap_hook_gyro_sample(const struct gyro_sample *state)
 void ap_hook_accel_sample(const struct accel_sample *state)
 {
     static uint64_t last_print_us;
+    static uint32_t counter;
+    static uint32_t fsync_count;
+    counter++;
+    if (state->fsync_set) {
+        fsync_count++;
+    }
     if (state->time_us - last_print_us < 1000000UL) {
         return;
     }
     last_print_us = state->time_us;
     // print accels once per second
-    printf("accel (%.1f,%.1f,%.1f)\n",
+    printf("accel (%.1f,%.1f,%.1f) %lu %lu\n",
            state->accel[0],
            state->accel[1],
-           state->accel[2]);
+           state->accel[2],
+           (unsigned long)counter,
+           (unsigned long)fsync_count);
 }