diff --git a/src/clock.cpp b/src/clock.cpp
index 93da90a8..63c0100a 100644
--- a/src/clock.cpp
+++ b/src/clock.cpp
@@ -195,6 +195,7 @@ uint64_t zmq::clock_t::now_us ()
 
 #else
 
+    LIBZMQ_UNUSED (nsecs_per_usec);
     //  Use POSIX gettimeofday function to get precise time.
     struct timeval tv;
     int rc = gettimeofday (&tv, NULL);