diff --git a/pkt-line.c b/pkt-line.c
index 657a702927..d633005ef7 100644
--- a/pkt-line.c
+++ b/pkt-line.c
@@ -461,9 +461,11 @@ int recv_sideband(const char *me, int in_stream, int out)
 	enum sideband_type sideband_type;
 
 	while (1) {
-		len = packet_read(in_stream, NULL, NULL, buf, LARGE_PACKET_MAX,
-				  0);
-		if (!demultiplex_sideband(me, buf, len, 0, &scratch,
+		int status = packet_read_with_status(in_stream, NULL, NULL,
+						     buf, LARGE_PACKET_MAX,
+						     &len,
+						     PACKET_READ_GENTLE_ON_EOF);
+		if (!demultiplex_sideband(me, status, buf, len, 0, &scratch,
 					  &sideband_type))
 			continue;
 		switch (sideband_type) {
@@ -520,9 +522,9 @@ enum packet_read_status packet_reader_read(struct packet_reader *reader)
 							 reader->options);
 		if (!reader->use_sideband)
 			break;
-		if (demultiplex_sideband(reader->me, reader->buffer,
-					 reader->pktlen, 1, &scratch,
-					 &sideband_type))
+		if (demultiplex_sideband(reader->me, reader->status,
+					 reader->buffer, reader->pktlen, 1,
+					 &scratch, &sideband_type))
 			break;
 	}
 
diff --git a/sideband.c b/sideband.c
index e337d76e80..81daddeb54 100644
--- a/sideband.c
+++ b/sideband.c
@@ -3,6 +3,7 @@
 #include "config.h"
 #include "sideband.h"
 #include "help.h"
+#include "pkt-line.h"
 
 struct keyword_entry {
 	/*
@@ -114,7 +115,8 @@ static void maybe_colorize_sideband(struct strbuf *dest, const char *src, int n)
 #define ANSI_SUFFIX "\033[K"
 #define DUMB_SUFFIX "        "
 
-int demultiplex_sideband(const char *me, char *buf, int len,
+int demultiplex_sideband(const char *me, int status,
+			 char *buf, int len,
 			 int die_on_error,
 			 struct strbuf *scratch,
 			 enum sideband_type *sideband_type)
@@ -130,17 +132,30 @@ int demultiplex_sideband(const char *me, char *buf, int len,
 			suffix = DUMB_SUFFIX;
 	}
 
-	if (len == 0) {
-		*sideband_type = SIDEBAND_FLUSH;
-		goto cleanup;
-	}
-	if (len < 1) {
+	if (status == PACKET_READ_EOF) {
 		strbuf_addf(scratch,
-			    "%s%s: protocol error: no band designator",
+			    "%s%s: unexpected disconnect while reading sideband packet",
 			    scratch->len ? "\n" : "", me);
 		*sideband_type = SIDEBAND_PROTOCOL_ERROR;
 		goto cleanup;
 	}
+
+	if (len < 0)
+		BUG("negative length on non-eof packet read");
+
+	if (len == 0) {
+		if (status == PACKET_READ_NORMAL) {
+			strbuf_addf(scratch,
+				    "%s%s: protocol error: missing sideband designator",
+				    scratch->len ? "\n" : "", me);
+			*sideband_type = SIDEBAND_PROTOCOL_ERROR;
+		} else {
+			/* covers flush, delim, etc */
+			*sideband_type = SIDEBAND_FLUSH;
+		}
+		goto cleanup;
+	}
+
 	band = buf[0] & 0xff;
 	buf[len] = '\0';
 	len--;
diff --git a/sideband.h b/sideband.h
index 227740a58e..5a25331be5 100644
--- a/sideband.h
+++ b/sideband.h
@@ -18,8 +18,12 @@ enum sideband_type {
  *
  * scratch must be a struct strbuf allocated by the caller. It is used to store
  * progress messages split across multiple packets.
+ *
+ * The "status" parameter is a pkt-line response as returned by
+ * packet_read_with_status() (e.g., PACKET_READ_NORMAL).
  */
-int demultiplex_sideband(const char *me, char *buf, int len,
+int demultiplex_sideband(const char *me, int status,
+			 char *buf, int len,
 			 int die_on_error,
 			 struct strbuf *scratch,
 			 enum sideband_type *sideband_type);
diff --git a/t/t0070-fundamental.sh b/t/t0070-fundamental.sh
index 357201640a..8d59905ef0 100755
--- a/t/t0070-fundamental.sh
+++ b/t/t0070-fundamental.sh
@@ -40,4 +40,16 @@ test_expect_success 'incomplete sideband messages are reassembled' '
 	grep "Hello, world" err
 '
 
+test_expect_success 'eof on sideband message is reported' '
+	printf 1234 >input &&
+	test-tool pkt-line receive-sideband <input 2>err &&
+	test_i18ngrep "unexpected disconnect" err
+'
+
+test_expect_success 'missing sideband designator is reported' '
+	printf 0004 >input &&
+	test-tool pkt-line receive-sideband <input 2>err &&
+	test_i18ngrep "missing sideband" err
+'
+
 test_done