diff -dur a/src/clock.cpp b/src/clock.cpp
--- a/src/clock.cpp	2021-07-12 21:15:35.111146311 +0000
+++ b/src/clock.cpp	2021-07-12 21:22:09.059753013 +0000
@@ -194,6 +194,7 @@
 #else

     //  Use POSIX gettimeofday function to get precise time.
+    LIBZMQ_UNUSED (nsecs_per_usec);
     struct timeval tv;
     int rc = gettimeofday (&tv, NULL);
     errno_assert (rc == 0);
