diff --git a/src/ip.cpp b/src/ip.cpp
index 45e54984..c194f0e4 100644
--- a/src/ip.cpp
+++ b/src/ip.cpp
@@ -73,11 +73,11 @@ zmq::fd_t zmq::open_socket (int domain_, int type_, int protocol_)
 
 void zmq::unblock_socket (fd_t s_)
 {
-#ifdef ZMQ_HAVE_WINDOWS
+#if defined ZMQ_HAVE_WINDOWS
     u_long nonblock = 1;
     int rc = ioctlsocket (s_, FIONBIO, &nonblock);
     wsa_assert (rc != SOCKET_ERROR);
-#elif ZMQ_HAVE_OPENVMS
+#elif defined ZMQ_HAVE_OPENVMS
     int nonblock = 1;
     int rc = ioctl (s_, FIONBIO, &nonblock);
     errno_assert (rc != -1);
diff --git a/src/zmq.cpp b/src/zmq.cpp
index 72bed06c..5e5ad58a 100644
--- a/src/zmq.cpp
+++ b/src/zmq.cpp
@@ -56,7 +56,7 @@
 
 
 // XSI vector I/O
-#if ZMQ_HAVE_UIO
+#if defined ZMQ_HAVE_UIO
 #include <sys/uio.h>
 #else
 struct iovec {