diff --git a/libraries/AP_Common/AP_Common.h b/libraries/AP_Common/AP_Common.h
index 48b2ae4293..f93fdc0706 100644
--- a/libraries/AP_Common/AP_Common.h
+++ b/libraries/AP_Common/AP_Common.h
@@ -159,24 +159,3 @@ bool is_bounded_int32(int32_t value, int32_t lower_bound, int32_t upper_bound);
 #else
 #define SITL_printf(fmt, args ...)
 #endif
-
-/*
-  a method to make semaphores less error prone
- */
-class WithSemaphore {
-public:
-    WithSemaphore(HAL_Semaphore &mtx) :
-    _mtx(mtx)
-    {
-        _mtx.take_blocking();
-    }
-
-    ~WithSemaphore() {
-        _mtx.give();
-    }
-private:
-    HAL_Semaphore &_mtx;
-};
-
-#define WITH_SEMAPHORE(sem) WithSemaphore _getsem(sem)
-
diff --git a/libraries/AP_Common/Semaphore.h b/libraries/AP_Common/Semaphore.h
new file mode 100644
index 0000000000..1e00dbf87a
--- /dev/null
+++ b/libraries/AP_Common/Semaphore.h
@@ -0,0 +1,37 @@
+/*
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/*
+  a method to make semaphores less error prone. The WITH_SEMAPHORE()
+  macro will block forever for a semaphore, and will automatically
+  release the semaphore when it goes out of scope
+ */
+class WithSemaphore {
+public:
+    WithSemaphore(HAL_Semaphore &mtx) :
+    _mtx(mtx)
+    {
+        _mtx.take_blocking();
+    }
+
+    ~WithSemaphore() {
+        _mtx.give();
+    }
+private:
+    HAL_Semaphore &_mtx;
+};
+
+#define WITH_SEMAPHORE(sem) WithSemaphore _getsem(sem)
+