diff --git a/misc.c b/misc.c
index 78d829a9..09e6db57 100644
--- a/misc.c
+++ b/misc.c
@@ -181,6 +181,8 @@ void bufchain_add(bufchain *ch, const void *data, int len)
 {
     const char *buf = (const char *)data;
 
+    if (len == 0) return;
+
     ch->buffersize += len;
 
     if (ch->tail && ch->tail->buflen < BUFFER_GRANULE) {
diff --git a/plink.c b/plink.c
index 41a5001e..f0fe60cf 100644
--- a/plink.c
+++ b/plink.c
@@ -180,8 +180,6 @@ int from_backend(void *frontend_handle, int is_stderr,
 {
     int osize, esize;
 
-    assert(len > 0);
-
     if (is_stderr) {
 	bufchain_add(&stderr_data, data, len);
 	try_output(1);
diff --git a/psftp.c b/psftp.c
index ca01f12a..c7cd8701 100644
--- a/psftp.c
+++ b/psftp.c
@@ -1639,14 +1639,13 @@ int from_backend(void *frontend, int is_stderr, const char *data, int datalen)
     unsigned char *p = (unsigned char *) data;
     unsigned len = (unsigned) datalen;
 
-    assert(len > 0);
-
     /*
      * stderr data is just spouted to local stderr and otherwise
      * ignored.
      */
     if (is_stderr) {
-	fwrite(data, 1, len, stderr);
+	if (len > 0)
+	    fwrite(data, 1, len, stderr);
 	return 0;
     }
 
@@ -1656,7 +1655,7 @@ int from_backend(void *frontend, int is_stderr, const char *data, int datalen)
     if (!outptr)
 	return 0;
 
-    if (outlen > 0) {
+    if ((outlen > 0) && (len > 0)) {
 	unsigned used = outlen;
 	if (used > len)
 	    used = len;
diff --git a/scp.c b/scp.c
index de394840..70f13be9 100644
--- a/scp.c
+++ b/scp.c
@@ -178,14 +178,13 @@ int from_backend(void *frontend, int is_stderr, const char *data, int datalen)
     unsigned char *p = (unsigned char *) data;
     unsigned len = (unsigned) datalen;
 
-    assert(len > 0);
-
     /*
      * stderr data is just spouted to local stderr and otherwise
      * ignored.
      */
     if (is_stderr) {
-	fwrite(data, 1, len, stderr);
+	if (len > 0)
+	    fwrite(data, 1, len, stderr);
 	return 0;
     }
 
@@ -195,7 +194,7 @@ int from_backend(void *frontend, int is_stderr, const char *data, int datalen)
     if (!outptr)
 	return 0;
 
-    if (outlen > 0) {
+    if ((outlen > 0) && (len > 0)) {
 	unsigned used = outlen;
 	if (used > len)
 	    used = len;
diff --git a/terminal.c b/terminal.c
index 5efe4842..1fa66e12 100644
--- a/terminal.c
+++ b/terminal.c
@@ -4792,8 +4792,6 @@ int term_ldisc(Terminal *term, int option)
 
 int term_data(Terminal *term, int is_stderr, const char *data, int len)
 {
-    assert(len > 0);
-
     bufchain_add(&term->inbuf, data, len);
 
     if (!term->in_term_out) {
diff --git a/unix/uxplink.c b/unix/uxplink.c
index d069e045..087c2d87 100644
--- a/unix/uxplink.c
+++ b/unix/uxplink.c
@@ -170,8 +170,6 @@ int from_backend(void *frontend_handle, int is_stderr,
 {
     int osize, esize;
 
-    assert(len > 0);
-
     if (is_stderr) {
 	bufchain_add(&stderr_data, data, len);
 	try_output(1);