diff --git a/include/libopencm3/cm3/sync.h b/include/libopencm3/cm3/sync.h
index 93c12bbd..6937ac63 100644
--- a/include/libopencm3/cm3/sync.h
+++ b/include/libopencm3/cm3/sync.h
@@ -22,6 +22,8 @@
 
 #include "common.h"
 
+BEGIN_DECLS
+
 void __dmb(void);
 
 /* Implements synchronisation primitives as discussed in the ARM document
@@ -52,4 +54,6 @@ void mutex_unlock(mutex_t *m);
 
 #endif
 
+END_DECLS
+
 #endif