diff --git a/headers/build/HaikuBuildCompatibility.h b/headers/build/HaikuBuildCompatibility.h
index 833ab8dbe7..7a852d4db9 100644
--- a/headers/build/HaikuBuildCompatibility.h
+++ b/headers/build/HaikuBuildCompatibility.h
@@ -119,20 +119,6 @@ struct media_node;
 extern "C" {
 #endif
 
-extern void		atomic_set(int32* value, int32 newValue);
-extern int32	atomic_get_and_set(int32* value, int32 newValue);
-extern int32	atomic_test_and_set(int32 *value, int32 newValue,
-					int32 testAgainst);
-extern int32	atomic_get(int32 *value);
-extern void		atomic_set64(int64* value, int64 newValue);
-extern int64	atomic_get_and_set64(int64* value, int64 newValue);
-extern int64	atomic_test_and_set64(int64 *value, int64 newValue,
-					int64 testAgainst);
-extern int64	atomic_get64(int64 *value);
-extern int64	atomic_add64(int64 *value, int64 addValue);
-extern int64	atomic_and64(int64 *value, int64 andValue);
-extern int64	atomic_or64(int64 *value, int64 orValue);
-
 extern size_t	strnlen(const char *string, size_t count);
 
 extern size_t	strlcat(char *dest, const char *source, size_t length);
diff --git a/headers/os/support/SupportDefs.h b/headers/os/support/SupportDefs.h
index 476d42c0ba..7e47018178 100644
--- a/headers/os/support/SupportDefs.h
+++ b/headers/os/support/SupportDefs.h
@@ -217,9 +217,6 @@ extern void*	get_stack_frame(void);
 
 #if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 7)
 
-#ifdef __cplusplus
-extern "C" {
-#endif
 
 static inline void
 atomic_set(int32* value, int32 newValue)
@@ -322,10 +319,6 @@ atomic_get64(int64* value)
 	return __atomic_load_n(value, __ATOMIC_ACQUIRE);
 }
 
-#ifdef __cplusplus
-}
-#endif
-
 
 #else	// __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 7)