diff --git a/t/t0081-line-buffer.sh b/t/t0081-line-buffer.sh
index 68d6163995..33a728ed98 100755
--- a/t/t0081-line-buffer.sh
+++ b/t/t0081-line-buffer.sh
@@ -1,10 +1,76 @@
 #!/bin/sh
 
 test_description="Test the svn importer's input handling routines.
+
+These tests exercise the line_buffer library, but their real purpose
+is to check the assumptions that library makes of the platform's input
+routines.  Processes engaged in bi-directional communication would
+hang if fread or fgets is too greedy.
+
+While at it, check that input of newlines and null bytes are handled
+correctly.
 "
 . ./test-lib.sh
 
-test_expect_success 'read greeting' '
+test -n "$GIT_REMOTE_SVN_TEST_BIG_FILES" && test_set_prereq EXPENSIVE
+
+generate_tens_of_lines () {
+	tens=$1 &&
+	line=$2 &&
+
+	i=0 &&
+	while test $i -lt "$tens"
+	do
+		for j in a b c d e f g h i j
+		do
+			echo "$line"
+		done &&
+		: $((i = $i + 1)) ||
+		return
+	done
+}
+
+long_read_test () {
+	: each line is 10 bytes, including newline &&
+	line=abcdefghi &&
+	echo "$line" >expect &&
+
+	if ! test_declared_prereq PIPE
+	then
+		echo >&4 "long_read_test: need to declare PIPE prerequisite"
+		return 127
+	fi &&
+	tens_of_lines=$(($1 / 100 + 1)) &&
+	lines=$(($tens_of_lines * 10)) &&
+	readsize=$((($lines - 1) * 10 + 3)) &&
+	copysize=7 &&
+	rm -f input &&
+	mkfifo input &&
+	{
+		{
+			generate_tens_of_lines $tens_of_lines "$line" &&
+			sleep 100
+		} >input &
+	} &&
+	test-line-buffer input <<-EOF >output &&
+	read $readsize
+	copy $copysize
+	EOF
+	kill $! &&
+	test_line_count = $lines output &&
+	tail -n 1 <output >actual &&
+	test_cmp expect actual
+}
+
+test_expect_success 'setup: have pipes?' '
+      rm -f frob &&
+      if mkfifo frob
+      then
+		test_set_prereq PIPE
+      fi
+'
+
+test_expect_success 'hello world' '
 	echo HELLO >expect &&
 	test-line-buffer <<-\EOF >actual &&
 	read 6
@@ -13,6 +79,21 @@ test_expect_success 'read greeting' '
 	test_cmp expect actual
 '
 
+test_expect_success PIPE '0-length read, no input available' '
+	>expect &&
+	rm -f input &&
+	mkfifo input &&
+	{
+		sleep 100 >input &
+	} &&
+	test-line-buffer input <<-\EOF >actual &&
+	read 0
+	copy 0
+	EOF
+	kill $! &&
+	test_cmp expect actual
+'
+
 test_expect_success '0-length read, send along greeting' '
 	echo HELLO >expect &&
 	test-line-buffer <<-\EOF >actual &&
@@ -23,6 +104,33 @@ test_expect_success '0-length read, send along greeting' '
 	test_cmp expect actual
 '
 
+test_expect_success PIPE '1-byte read, no input available' '
+	printf "%s" ab >expect &&
+	rm -f input &&
+	mkfifo input &&
+	{
+		{
+			printf "%s" a &&
+			printf "%s" b &&
+			sleep 100
+		} >input &
+	} &&
+	test-line-buffer input <<-\EOF >actual &&
+	read 1
+	copy 1
+	EOF
+	kill $! &&
+	test_cmp expect actual
+'
+
+test_expect_success PIPE 'long read (around 8192 bytes)' '
+	long_read_test 8192
+'
+
+test_expect_success PIPE,EXPENSIVE 'longer read (around 65536 bytes)' '
+	long_read_test 65536
+'
+
 test_expect_success 'buffer_read_string copes with null byte' '
 	>expect &&
 	q_to_nul <<-\EOF | test-line-buffer >actual &&
diff --git a/test-line-buffer.c b/test-line-buffer.c
index da0bc6502c..ec19b13ee2 100644
--- a/test-line-buffer.c
+++ b/test-line-buffer.c
@@ -49,15 +49,31 @@ static void handle_line(const char *line, struct line_buffer *stdin_buf)
 int main(int argc, char *argv[])
 {
 	struct line_buffer stdin_buf = LINE_BUFFER_INIT;
+	struct line_buffer file_buf = LINE_BUFFER_INIT;
+	struct line_buffer *input = &stdin_buf;
+	const char *filename;
 	char *s;
 
-	if (argc != 1)
-		usage("test-line-buffer < script");
+	if (argc == 1)
+		filename = NULL;
+	else if (argc == 2)
+		filename = argv[1];
+	else
+		usage("test-line-buffer [file] < script");
 
 	if (buffer_init(&stdin_buf, NULL))
 		die_errno("open error");
+	if (filename) {
+		if (buffer_init(&file_buf, filename))
+			die_errno("error opening %s", filename);
+		input = &file_buf;
+	}
+
 	while ((s = buffer_read_line(&stdin_buf)))
-		handle_line(s, &stdin_buf);
+		handle_line(s, input);
+
+	if (filename && buffer_deinit(&file_buf))
+		die("error reading from %s", filename);
 	if (buffer_deinit(&stdin_buf))
 		die("input error");
 	if (ferror(stdout))