diff --git a/include/nuttx/fs/fs.h b/include/nuttx/fs/fs.h
index 82de23a8707..23313d97863 100644
--- a/include/nuttx/fs/fs.h
+++ b/include/nuttx/fs/fs.h
@@ -73,16 +73,21 @@
  * (libuc.a and libunx.a).  The that case, the correct interface must be
  * used for the build context.
  *
- * The interfaces open(), close(), creat(), read(), pread(), write(),
- * pwrite(), poll(), select(), fcntl(), and aio_suspend() are all
- * cancellation points.
+ * REVISIT:  In the flat build, the same functions must be used both by
+ * the OS and by applications.  We have to use the normal user functions
+ * in this case or we will fail to set the errno or fail to create the
+ * cancellation point.
+ *
+ * The interfaces close(), creat(), read(), pread(), write(), pwrite(),
+ * poll(), select(), fcntl(), and aio_suspend() are all cancellation
+ * points.
  *
  * REVISIT:  These cancellation points are an issue and may cause
  * violations:  It use of these internally will cause the calling function
  * to become a cancellation points!
  */
 
-#if defined(CONFIG_BUILD_FLAT) || defined(__KERNEL__)
+#if !defined(CONFIG_BUILD_FLAT) && defined(__KERNEL__)
 #  ifdef CONFIG_CPP_HAVE_VARARGS
 #    define _NX_OPEN(p,f,...)  nx_open(p,f,##__VA_ARGS__)
 #  else
diff --git a/include/nuttx/mqueue.h b/include/nuttx/mqueue.h
index 9c6a650c287..c33f1768aa5 100644
--- a/include/nuttx/mqueue.h
+++ b/include/nuttx/mqueue.h
@@ -68,15 +68,13 @@
  * (libuc.a and libunx.a).  The that case, the correct interface must be
  * used for the build context.
  *
- * The interfaces sigtimedwait(), sigwait(), sigwaitinfo(), sleep(),
- * nanosleep(), and usleep()  are cancellation points.
- *
- * REVISIT:  The fact that these interfaces are cancellation points is an
- * issue and may cause violations:  It use of these internally will cause
- * the calling function to become a cancellation points!
+ * REVISIT:  In the flat build, the same functions must be used both by
+ * the OS and by applications.  We have to use the normal user functions
+ * in this case or we will fail to set the errno or fail to create the
+ * cancellation point.
  */
 
-#if defined(CONFIG_BUILD_FLAT) || defined(__KERNEL__)
+#if !defined(CONFIG_BUILD_FLAT) && defined(__KERNEL__)
 #  define _MQ_SEND(d,m,l,p)           nxmq_send(d,m,l,p)
 #  define _MQ_TIMEDSEND(d,m,l,p,t)    nxmq_timedsend(d,m,l,p,t)
 #  define _MQ_RECEIVE(d,m,l,p)        nxmq_receive(d,m,l,p)
diff --git a/include/nuttx/net/net.h b/include/nuttx/net/net.h
index 93569abae1c..081424bb12e 100644
--- a/include/nuttx/net/net.h
+++ b/include/nuttx/net/net.h
@@ -65,6 +65,11 @@
  * (libuc.a and libunx.a).  The that case, the correct interface must be
  * used for the build context.
  *
+ * REVISIT:  In the flat build, the same functions must be used both by
+ * the OS and by applications.  We have to use the normal user functions
+ * in this case or we will fail to set the errno or fail to create the
+ * cancellation point.
+ *
  * The interfaces accept(), read(), recv(), recvfrom(), write(), send(),
  * sendto() are all cancellation points.
  *
@@ -73,7 +78,7 @@
  * to become a cancellation points!
  */
 
-#if defined(CONFIG_BUILD_FLAT) || defined(__KERNEL__)
+#if !defined(CONFIG_BUILD_FLAT) && defined(__KERNEL__)
 #  define _NX_SEND(s,b,l,f)         nx_send(s,b,l,f)
 #  define _NX_RECV(s,b,l,f)         nx_recv(s,b,l,f)
 #  define _NX_RECVFROM(s,b,l,f,a,n) nx_recvfrom(s,b,l,f,a,n)
diff --git a/include/nuttx/sched.h b/include/nuttx/sched.h
index ebac8152ac3..17fb3706226 100644
--- a/include/nuttx/sched.h
+++ b/include/nuttx/sched.h
@@ -188,9 +188,14 @@
  * used both by the OS (libkc.a and libknx.a) or by the applications
  * (libuc.a and libunx.a).  The that case, the correct interface must be
  * used for the build context.
+ *
+ * REVISIT:  In the flat build, the same functions must be used both by
+ * the OS and by applications.  We have to use the normal user functions
+ * in this case or we will fail to set the errno or fail to create the
+ * cancellation point.
  */
 
-#if defined(CONFIG_BUILD_FLAT) || defined(__KERNEL__)
+#if !defined(CONFIG_BUILD_FLAT) && defined(__KERNEL__)
 #  define _SCHED_GETPARAM(t,p)       nxsched_getparam(t,p)
 #  define _SCHED_SETPARAM(t,p)       nxsched_setparam(t,p)
 #  define _SCHED_GETSCHEDULER(t)     nxsched_getscheduler(t)
diff --git a/include/nuttx/semaphore.h b/include/nuttx/semaphore.h
index 4a44f2f4ea6..0b0fc8dbf69 100644
--- a/include/nuttx/semaphore.h
+++ b/include/nuttx/semaphore.h
@@ -68,14 +68,13 @@
  * (libuc.a and libunx.a).  The that case, the correct interface must be
  * used for the build context.
  *
- * The interfaces sem_wait() and sem_timedwait() are cancellation points.
- *
- * REVISIT:  The fact that sem_wait() and sem_timedwait() are cancellation
- * points is an issue and may cause violations:  It use of these internally
- * will cause the calling function to become a cancellation points!
+ * REVISIT:  In the flat build, the same functions must be used both by
+ * the OS and by applications.  We have to use the normal user functions
+ * in this case or we will fail to set the errno or fail to create the
+ * cancellation point.
  */
 
-#if defined(CONFIG_BUILD_FLAT) || defined(__KERNEL__)
+#if !defined(CONFIG_BUILD_FLAT) && defined(__KERNEL__)
 #  define _SEM_INIT(s,p,c)      nxsem_init(s,p,c)
 #  define _SEM_DESTROY(s)       nxsem_destroy(s)
 #  define _SEM_WAIT(s)          nxsem_wait(s)
diff --git a/include/nuttx/signal.h b/include/nuttx/signal.h
index fda07825a6f..8d48adda23c 100644
--- a/include/nuttx/signal.h
+++ b/include/nuttx/signal.h
@@ -61,6 +61,11 @@
  * (libuc.a and libunx.a).  The that case, the correct interface must be
  * used for the build context.
  *
+ * REVISIT:  In the flat build, the same functions must be used both by
+ * the OS and by applications.  We have to use the normal user functions
+ * in this case or we will fail to set the errno or fail to create the
+ * cancellation point.
+ *
  * The interfaces sigtimedwait(), sigwait(), sigwaitinfo(), sleep(),
  * nanosleep(), and usleep()  are cancellation points.
  *
@@ -69,7 +74,7 @@
  * the calling function to become a cancellation points!
  */
 
-#if defined(CONFIG_BUILD_FLAT) || defined(__KERNEL__)
+#if !defined(CONFIG_BUILD_FLAT) && defined(__KERNEL__)
 #  define _SIG_PROCMASK(h,s,o)  nxsig_procmask(h,s,o)
 #  define _SIG_SIGACTION(s,a,o) nxsig_action(s,a,o,false)
 #  define _SIG_QUEUE(p,s,v)     nxsig_queue(p,s,v)