diff --git a/libraries/AP_Compass/AP_Compass_HMC5843.cpp b/libraries/AP_Compass/AP_Compass_HMC5843.cpp
index 4418efeebc..5c1bd6b0bf 100644
--- a/libraries/AP_Compass/AP_Compass_HMC5843.cpp
+++ b/libraries/AP_Compass/AP_Compass_HMC5843.cpp
@@ -197,6 +197,27 @@ bool AP_Compass_HMC5843::re_initialise()
 }
 
 
+bool AP_Compass_HMC5843::_detect_version()
+{
+    _base_config = 0x0;
+
+    if (!write_register(ConfigRegA, SampleAveraging_8<<5 | DataOutputRate_75HZ<<2 | NormalOperation) ||
+        !read_register(ConfigRegA, &_base_config)) {
+        return false;
+    }
+    if (_base_config == (SampleAveraging_8<<5 | DataOutputRate_75HZ<<2 | NormalOperation)) {
+        /* a 5883L supports the sample averaging config */
+        _product_id = AP_COMPASS_TYPE_HMC5883L;
+        return true;
+    } else if (_base_config == (NormalOperation | DataOutputRate_75HZ<<2)) {
+        _product_id = AP_COMPASS_TYPE_HMC5843;
+        return true;
+    } else {
+        /* not behaving like either supported compass type */
+        return false;
+    }
+}
+
 // Public Methods //////////////////////////////////////////////////////////////
 bool
 AP_Compass_HMC5843::init()
@@ -216,17 +237,11 @@ AP_Compass_HMC5843::init()
         hal.scheduler->panic(PSTR("Failed to get HMC5843 semaphore"));
     }
 
-    // determine if we are using 5843 or 5883L
-    _base_config = 0;
-    if (!write_register(ConfigRegA, SampleAveraging_8<<5 | DataOutputRate_75HZ<<2 | NormalOperation) ||
-        !read_register(ConfigRegA, &_base_config)) {
-        _i2c_sem->give();
-        hal.scheduler->resume_timer_procs();
-        return false;
+    if (!_detect_version()) {
+        goto errout;
     }
-    if ( _base_config == (SampleAveraging_8<<5 | DataOutputRate_75HZ<<2 | NormalOperation)) {
-        // a 5883L supports the sample averaging config
-        _product_id = AP_COMPASS_TYPE_HMC5883L;
+
+    if (_product_id == AP_COMPASS_TYPE_HMC5883L) {
         calibration_gain = 0x60;
         /*
           note that the HMC5883 datasheet gives the x and y expected
@@ -236,13 +251,6 @@ AP_Compass_HMC5843::init()
         expected_x = 766;
         expected_yz  = 713;
         gain_multiple = 660.0f / 1090;  // adjustment for runtime vs calibration gain
-    } else if (_base_config == (NormalOperation | DataOutputRate_75HZ<<2)) {
-        _product_id = AP_COMPASS_TYPE_HMC5843;
-    } else {
-        // not behaving like either supported compass type
-        _i2c_sem->give();
-        hal.scheduler->resume_timer_procs();
-        return false;
     }
 
     calibration[0] = 0;
@@ -351,6 +359,12 @@ AP_Compass_HMC5843::init()
     }
 
     return success;
+
+errout:
+
+    _i2c_sem->give();
+    hal.scheduler->resume_timer_procs();
+    return false;
 }
 
 // Read Sensor data
diff --git a/libraries/AP_Compass/AP_Compass_HMC5843.h b/libraries/AP_Compass/AP_Compass_HMC5843.h
index 314c473906..c710d069b7 100644
--- a/libraries/AP_Compass/AP_Compass_HMC5843.h
+++ b/libraries/AP_Compass/AP_Compass_HMC5843.h
@@ -19,6 +19,9 @@ private:
     bool                re_initialise(void);
     bool                read_register(uint8_t address, uint8_t *value);
     bool                write_register(uint8_t address, uint8_t value);
+
+    bool                _detect_version();
+
     uint32_t            _retry_time; // when unhealthy the millis() value to retry at
     AP_HAL::Semaphore*  _i2c_sem;