diff --git a/CHANGES b/CHANGES
index f1b79b6..8e5fb7a 100644
--- a/CHANGES
+++ b/CHANGES
@@ -166,6 +166,10 @@ Features:
 	Filan prints the current value.
 	Tests: STDIN_F_SETPIPE_SZ EXEC_F_SETPIPE_SZ
 
+	Bidirectional PIPE addresses may block on writing a data chunk larger
+	than pipe buffer. Socat now tries to detect if transfer block size is
+	large enough and issues a warning.
+
 Corrections:
 	When a sub process (EXEC, SYSTEM) terminated with exit code other than
 	0, its last sent data might have been lost depending on timing of read/
diff --git a/socat.c b/socat.c
index 8632093..c857b0b 100644
--- a/socat.c
+++ b/socat.c
@@ -22,10 +22,11 @@
 #include "xioopts.h"
 #include "xiolockfile.h"
 
+#include "xio-pipe.h"
+
 
 /* command line options */
-struct {
-   size_t bufsiz;
+struct socat_opts {
    bool verbose;
    bool verbhex;
    struct timeval pollintv;	/* with ignoreeof, reread after seconds */
@@ -40,7 +41,6 @@ struct {
    unsigned long log_sigs;	/* signals to be caught just for logging */
    bool statistics; 	/* log statistics on exit */
 } socat_opts = {
-   8192,	/* bufsiz */
    false,	/* verbose */
    false,	/* verbhex */
    {1,0},	/* pollintv */
@@ -234,7 +234,7 @@ int main(int argc, const char *argv[]) {
 	       Exit(1);
 	    }
 	 }
-	 socat_opts.bufsiz = Strtoul(a, (char **)&a, 0, "-b");
+	 xioparms.bufsiz = Strtoul(a, (char **)&a, 0, "-b");
 	 break;
       case 's':  if (arg1[0][2])  { socat_opt_hint(stderr, arg1[0][1], arg1[0][2]); Exit(1); }
 	 diag_set_int('e', E_FATAL); break;
@@ -936,9 +936,9 @@ int _socat(void) {
 #endif /* WITH_FILAN */
 
    /* when converting nl to crnl, size might double */
-   if (socat_opts.bufsiz > (SIZE_MAX-1)/2) {
-      Error2("buffer size option (-b) to big - "F_Zu" (max is "F_Zu")", socat_opts.bufsiz, (SIZE_MAX-1)/2);
-      socat_opts.bufsiz = (SIZE_MAX-1)/2;
+   if (xioparms.bufsiz > (SIZE_MAX-1)/2) {
+      Error2("buffer size option (-b) to big - "F_Zu" (max is "F_Zu")", xioparms.bufsiz, (SIZE_MAX-1)/2);
+      xioparms.bufsiz = (SIZE_MAX-1)/2;
    }
 
 #if HAVE_PROTOTYPE_LIB_posix_memalign
@@ -946,13 +946,13 @@ int _socat(void) {
       Without this, eg.read() fails with "Invalid argument" */
    {
       int _errno;
-      if ((_errno = Posix_memalign((void **)&buff, getpagesize(), 2*socat_opts.bufsiz+1)) != 0) {
+      if ((_errno = Posix_memalign((void **)&buff, getpagesize(), 2*xioparms.bufsiz+1)) != 0) {
 	 Error1("posix_memalign(): %s", strerror(_errno));
 	 return -1;
       }
    }
 #else /* !HAVE_PROTOTYPE_LIB_posix_memalign */
-   buff = Malloc(2*socat_opts.bufsiz+1);
+   buff = Malloc(2*xioparms.bufsiz+1);
    if (buff == NULL)  return -1;
 #endif /* !HAVE_PROTOTYPE_LIB_posix_memalign */
 
@@ -1180,7 +1180,7 @@ int _socat(void) {
 
       if (mayrd1 && maywr2) {
 	 mayrd1 = false;
-	 if ((bytes1 = xiotransfer(sock1, sock2, buff, socat_opts.bufsiz, false))
+	 if ((bytes1 = xiotransfer(sock1, sock2, buff, xioparms.bufsiz, false))
 	     < 0) {
 	    if (errno != EAGAIN) {
 	       closing = MAX(closing, 1);
@@ -1212,7 +1212,7 @@ int _socat(void) {
 
       if (mayrd2 && maywr1) {
 	 mayrd2 = false;
-	 if ((bytes2 = xiotransfer(sock2, sock1, buff, socat_opts.bufsiz, true))
+	 if ((bytes2 = xiotransfer(sock2, sock1, buff, xioparms.bufsiz, true))
 	     < 0) {
 	    if (errno != EAGAIN) {
 	       closing = MAX(closing, 1);
@@ -1633,7 +1633,7 @@ int cv_newline(unsigned char *buff, ssize_t *bytes,
 	 from = '\r';
       }
       if (buf2 == NULL) {
-	 if ((buf2 = Malloc(socat_opts.bufsiz)) == NULL) {
+	 if ((buf2 = Malloc(xioparms.bufsiz)) == NULL) {
 	    return -1;
 	 }
       }
diff --git a/xio-pipe.c b/xio-pipe.c
index 718333f..da17b8a 100644
--- a/xio-pipe.c
+++ b/xio-pipe.c
@@ -74,6 +74,9 @@ static int xioopen_fifo_unnamed(xiofile_t *sock, struct opt *opts) {
       showleft(opts);
       Error1("INTERNAL: %d option(s) remained unused", numleft);
    }
+
+   xio_chk_pipesz(sfd->fd);
+
    Notice("writing to and reading from unnamed pipe");
    return 0;
 }
@@ -183,7 +186,45 @@ static int xioopen_fifo(
    applyopts_named(pipename, opts, PH_FD);
    applyopts(sfd, -1, opts, PH_FD);
    applyopts_cloexec(sfd->fd, opts);
+   xio_chk_pipesz(sfd->fd);
+
    return _xio_openlate(sfd, opts);
 }
 
+
+/* Checks if fd is a pipe and if its buffer is at least the blksiz.
+   returns 0 if ok;
+   returns 1 if unknown;
+   returns -1 if not */
+int xio_chk_pipesz(
+	int fd)
+{
+	struct stat st;
+	int pipesz;
+
+	if (fstat(fd, &st) < 0) {
+		Warn2("fstat(%d, ...): %s", fd, strerror(errno));
+		return 1;
+	}
+	if ((st.st_mode&S_IFMT) != S_IFIFO) {
+		return 0;
+	}
+
+#if defined(F_GETPIPE_SZ)
+	if ((pipesz = Fcntl(fd, F_GETPIPE_SZ)) < 0) {
+		Warn2("fcntl(%d, F_GETPIPE_SZ): %s", fd, strerror(errno));
+		return 1;
+	}
+
+	if (pipesz >= xioparms.bufsiz)
+		return 0;
+
+	Warn3("xio_chk_pipesz(%d, ...): Socat block size "F_Zu" is larger than pipe size %d, might block; use option f-setpipe-sz!",
+	      fd, xioparms.bufsiz, pipesz);
+	return -1;
+#else /* !defined(F_GETPIPE_SZ) */
+	return 1;
+#endif /* !defined(F_GETPIPE_SZ) */
+}
+
 #endif /* WITH_PIPE */
diff --git a/xio-pipe.h b/xio-pipe.h
index 7171e6b..ef3e06b 100644
--- a/xio-pipe.h
+++ b/xio-pipe.h
@@ -9,4 +9,6 @@ extern const struct addrdesc xioaddr_pipe;
 
 extern const struct optdesc opt_f_setpipe_sz;
 
+extern int xio_chk_pipesz(int fd);
+
 #endif /* !defined(__xio_pipe_h_included) */
diff --git a/xio-progcall.c b/xio-progcall.c
index 5a0f54d..9b302f0 100644
--- a/xio-progcall.c
+++ b/xio-progcall.c
@@ -330,7 +330,7 @@ int _xioopen_foxec(int xioflags,	/* XIO_RDONLY etc. */
       if (rw != XIO_RDONLY) {
 	 applyopts_cloexec(wrpip[1], popts);
 	 if (sfd->dtype == XIODATA_2PIPE)
-	    applyopts(NULL, wrpip[1], popts, PH_FD);
+	    applyopts(NULL, wrpip[1], popts2, PH_FD);
 	 else
 	    applyopts(NULL, wrpip[1], popts, PH_FD);
 	 applyopts(NULL, wrpip[0], copts, PH_FD);
diff --git a/xio.h b/xio.h
index 9af9d96..71bddc6 100644
--- a/xio.h
+++ b/xio.h
@@ -104,7 +104,7 @@ typedef uint32_t groups_t;
 #endif
 
 /* global XIO options/parameters */
-typedef struct {
+typedef struct xioparms {
    bool strictopts;
    const char *pipesep;
    const char *paramsep;
@@ -119,6 +119,7 @@ typedef struct {
    bool experimental;	/* enable some features */
    const char *sniffleft_name; 		/* file name with -r */
    const char *sniffright_name; 	/* file name with -R */
+   size_t bufsiz;
 } xioparms_t;
 
 /* pack the description of a lock file */
diff --git a/xioparam.c b/xioparam.c
index 11830c5..b2b1406 100644
--- a/xioparam.c
+++ b/xioparam.c
@@ -23,7 +23,8 @@ xioparms_t xioparms = {
    WITH_DEFAULT_IPV, 	/* preferred_ip */
    false, 	/* experimental */
    NULL, 	/* sniffleft_name */
-   NULL 	/* sniffright_name */
+   NULL, 	/* sniffright_name */
+   8192 	/* bufsiz */
 } ;