diff --git a/configure.ac b/configure.ac
index 414208da4..45948110c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1167,7 +1167,9 @@ AC_CHECK_FUNCS([          \
 	backtrace             \
 	fadvise               \
 	madvise               \
+	mlock                 \
 	mlock2                \
+	mmap                  \
 	posix_fadvise         \
 	posix_madvise         \
 	preadv2               \
diff --git a/ircd/fs.cc b/ircd/fs.cc
index 5fe291d6c..8938c9aa5 100644
--- a/ircd/fs.cc
+++ b/ircd/fs.cc
@@ -2061,10 +2061,14 @@ ircd::fs::map::map(const fd &fd,
 		size?: fs::size(fd)
 	};
 
+	#ifdef HAVE_MMAP
 	void *const &ptr
 	{
 		::mmap(nullptr, map_size, prot(opts), flags(opts), int(fd), opts.offset)
 	};
+	#else
+	#error "Missing ::mmap(2) on this platform."
+	#endif
 
 	if(unlikely(ptr == MAP_FAILED))
 		throw_system_error(errno);