Index: uspace/lib/c/include/atomic.h
===================================================================
--- uspace/lib/c/include/atomic.h	(revision ffa73c60dc2eba8ce632c52a0be8bbf4ecd562d9)
+++ uspace/lib/c/include/atomic.h	(revision 4621d2311994bf63dea425ed923239d4ca1babc9)
@@ -42,4 +42,6 @@
 typedef size_t atomic_count_t;
 typedef ssize_t atomic_signed_t;
+
+#define PRIua  "zu"          /**< Format for atomic_count_t. */
 
 typedef struct atomic {