diff --git a/src/assuan.h.in b/src/assuan.h.in
--- a/src/assuan.h.in
+++ b/src/assuan.h.in
@@ -546,7 +547,9 @@
 
 #define ASSUAN_SYSTEM_NPTH_IMPL						\
   static void _assuan_npth_usleep (assuan_context_t ctx, unsigned int usec) \
-  { (void) ctx; npth_usleep (usec); }					\
+  { ssize_t res; (void) ctx; npth_unprotect();				\
+    res = __assuan_usleep (ctx, usec);					\
+    npth_protect(); }							\
   static ssize_t _assuan_npth_read (assuan_context_t ctx, assuan_fd_t fd, \
 				    void *buffer, size_t size)		\
   { ssize_t res; (void) ctx; npth_unprotect();				\