diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index 68313424ee..c38234527f 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -6263,7 +6263,7 @@ InitPostmasterDeathWatchHandle(void)
 	 * write fd. That is taken care of in ClosePostmasterPorts().
 	 */
 	Assert(MyProcPid == PostmasterPid);
-	if (pipe(postmaster_alive_fds))
+	if (pipe(postmaster_alive_fds) < 0)
 		ereport(FATAL,
 				(errcode_for_file_access(),
 				 errmsg_internal("could not create pipe to monitor postmaster death: %m")));
@@ -6272,7 +6272,7 @@ InitPostmasterDeathWatchHandle(void)
 	 * Set O_NONBLOCK to allow testing for the fd's presence with a read()
 	 * call.
 	 */
-	if (fcntl(postmaster_alive_fds[POSTMASTER_FD_WATCH], F_SETFL, O_NONBLOCK))
+	if (fcntl(postmaster_alive_fds[POSTMASTER_FD_WATCH], F_SETFL, O_NONBLOCK) == -1)
 		ereport(FATAL,
 				(errcode_for_socket_access(),
 				 errmsg_internal("could not set postmaster death monitoring pipe to nonblocking mode: %m")));
diff --git a/src/backend/storage/ipc/latch.c b/src/backend/storage/ipc/latch.c
index 47983704d7..67162fdd4a 100644
--- a/src/backend/storage/ipc/latch.c
+++ b/src/backend/storage/ipc/latch.c
@@ -169,9 +169,9 @@ InitializeLatchSupport(void)
 	 */
 	if (pipe(pipefd) < 0)
 		elog(FATAL, "pipe() failed: %m");
-	if (fcntl(pipefd[0], F_SETFL, O_NONBLOCK) < 0)
+	if (fcntl(pipefd[0], F_SETFL, O_NONBLOCK) == -1)
 		elog(FATAL, "fcntl() failed on read-end of self-pipe: %m");
-	if (fcntl(pipefd[1], F_SETFL, O_NONBLOCK) < 0)
+	if (fcntl(pipefd[1], F_SETFL, O_NONBLOCK) == -1)
 		elog(FATAL, "fcntl() failed on write-end of self-pipe: %m");
 
 	selfpipe_readfd = pipefd[0];
diff --git a/src/bin/pg_test_fsync/pg_test_fsync.c b/src/bin/pg_test_fsync/pg_test_fsync.c
index d65c0ab110..266b2b6e41 100644
--- a/src/bin/pg_test_fsync/pg_test_fsync.c
+++ b/src/bin/pg_test_fsync/pg_test_fsync.c
@@ -7,6 +7,7 @@
 
 #include <sys/stat.h>
 #include <sys/time.h>
+#include <fcntl.h>
 #include <time.h>
 #include <unistd.h>
 #include <signal.h>
diff --git a/src/port/noblock.c b/src/port/noblock.c
index 7e70319bd4..673fa8aa3c 100644
--- a/src/port/noblock.c
+++ b/src/port/noblock.c
@@ -1,7 +1,7 @@
 /*-------------------------------------------------------------------------
  *
  * noblock.c
- *	  set a file descriptor as non-blocking
+ *	  set a file descriptor as blocking or non-blocking
  *
  * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
@@ -17,11 +17,22 @@
 #include <fcntl.h>
 
 
+/*
+ * Put socket into nonblock mode.
+ * Returns true on success, false on failure.
+ */
 bool
 pg_set_noblock(pgsocket sock)
 {
 #if !defined(WIN32)
-	return (fcntl(sock, F_SETFL, O_NONBLOCK) != -1);
+	int			flags;
+
+	flags = fcntl(sock, F_GETFL);
+	if (flags < 0)
+		return false;
+	if (fcntl(sock, F_SETFL, (flags | O_NONBLOCK)) == -1)
+		return false;
+	return true;
 #else
 	unsigned long ioctlsocket_ret = 1;
 
@@ -30,7 +41,10 @@ pg_set_noblock(pgsocket sock)
 #endif
 }
 
-
+/*
+ * Put socket into blocking mode.
+ * Returns true on success, false on failure.
+ */
 bool
 pg_set_block(pgsocket sock)
 {
@@ -38,7 +52,9 @@ pg_set_block(pgsocket sock)
 	int			flags;
 
 	flags = fcntl(sock, F_GETFL);
-	if (flags < 0 || fcntl(sock, F_SETFL, (long) (flags & ~O_NONBLOCK)))
+	if (flags < 0)
+		return false;
+	if (fcntl(sock, F_SETFL, (flags & ~O_NONBLOCK)) == -1)
 		return false;
 	return true;
 #else