diff --git a/Makefile b/Makefile
index 958828545..68979e6b2 100644
--- a/Makefile
+++ b/Makefile
@@ -114,6 +114,7 @@ TEST_PROGS  := \
 	basename \
 	cat \
 	cksum \
+	comm \
 	cp \
 	cut \
 	dirname \
diff --git a/src/comm/comm.rs b/src/comm/comm.rs
index ee37afd94..75528942b 100644
--- a/src/comm/comm.rs
+++ b/src/comm/comm.rs
@@ -72,6 +72,7 @@ fn comm(a: &mut LineReader, b: &mut LineReader, opts: &getopts::Matches) {
             (false, true)  => Ordering::Greater,
             (true , false) => Ordering::Less,
             (true , true) => match(&na, &nb) {
+                (&Ok(0), &Ok(0)) => break,
                 (&Ok(0), _) => Ordering::Greater,
                 (_, &Ok(0)) => Ordering::Less,
                 _ =>  ra.cmp(&rb),
@@ -85,6 +86,7 @@ fn comm(a: &mut LineReader, b: &mut LineReader, opts: &getopts::Matches) {
                     ensure_nl(ra);
                     print!("{}{}", delim[1], ra);
                 }
+                ra.clear();
                 na = a.read_line(ra);
             },
             Ordering::Greater => {
@@ -92,6 +94,7 @@ fn comm(a: &mut LineReader, b: &mut LineReader, opts: &getopts::Matches) {
                     ensure_nl(rb);
                     print!("{}{}", delim[2], rb);
                 }
+                rb.clear();
                 nb = b.read_line(rb);
             },
             Ordering::Equal => {
@@ -99,6 +102,8 @@ fn comm(a: &mut LineReader, b: &mut LineReader, opts: &getopts::Matches) {
                     ensure_nl(ra);
                     print!("{}{}", delim[3], ra);
                 }
+                ra.clear();
+                rb.clear();
                 na = a.read_line(ra);
                 nb = b.read_line(rb);
             }
diff --git a/tests/comm.rs b/tests/comm.rs
new file mode 100644
index 000000000..390d50b89
--- /dev/null
+++ b/tests/comm.rs
@@ -0,0 +1,47 @@
+#[macro_use] mod common;
+
+use common::util;
+
+static UTIL_NAME: &'static str = "comm";
+
+#[test]
+fn test_comm_ab_no_args() {
+    let (at, mut ucmd) = util::testing(UTIL_NAME);
+    let result = ucmd.args(&["a", "b"]).run();
+    assert_eq!(result.stdout, at.read("ab.expected"));
+}
+
+#[test]
+fn test_comm_ab_dash_one() {
+    let (at, mut ucmd) = util::testing(UTIL_NAME);
+    let result = ucmd.args(&["a", "b", "-1"]).run();
+    assert_eq!(result.stdout, at.read("ab1.expected"));
+}
+
+#[test]
+fn test_comm_ab_dash_two() {
+    let (at, mut ucmd) = util::testing(UTIL_NAME);
+    let result = ucmd.args(&["a", "b", "-2"]).run();
+    assert_eq!(result.stdout, at.read("ab2.expected"));
+}
+
+#[test]
+fn test_comm_ab_dash_three() {
+    let (at, mut ucmd) = util::testing(UTIL_NAME);
+    let result = ucmd.args(&["a", "b", "-3"]).run();
+    assert_eq!(result.stdout, at.read("ab3.expected"));
+}
+
+#[test]
+fn test_comm_aempty() {
+    let (at, mut ucmd) = util::testing(UTIL_NAME);
+    let result = ucmd.args(&["a", "empty"]).run();
+    assert_eq!(result.stdout, at.read("aempty.expected"));
+}
+
+#[test]
+fn test_comm_emptyempty() {
+    let (at, mut ucmd) = util::testing(UTIL_NAME);
+    let result = ucmd.args(&["empty", "empty"]).run();
+    assert_eq!(result.stdout, at.read("emptyempty.expected"));
+}
diff --git a/tests/fixtures/comm/a b/tests/fixtures/comm/a
new file mode 100644
index 000000000..58f424cdb
--- /dev/null
+++ b/tests/fixtures/comm/a
@@ -0,0 +1,2 @@
+a
+z
diff --git a/tests/fixtures/comm/ab.expected b/tests/fixtures/comm/ab.expected
new file mode 100644
index 000000000..0efac0666
--- /dev/null
+++ b/tests/fixtures/comm/ab.expected
@@ -0,0 +1,3 @@
+a
+	b
+		z
diff --git a/tests/fixtures/comm/ab1.expected b/tests/fixtures/comm/ab1.expected
new file mode 100644
index 000000000..7c81c8ba7
--- /dev/null
+++ b/tests/fixtures/comm/ab1.expected
@@ -0,0 +1,2 @@
+b
+	z
diff --git a/tests/fixtures/comm/ab2.expected b/tests/fixtures/comm/ab2.expected
new file mode 100644
index 000000000..c98cd0da6
--- /dev/null
+++ b/tests/fixtures/comm/ab2.expected
@@ -0,0 +1,2 @@
+a
+	z
diff --git a/tests/fixtures/comm/ab3.expected b/tests/fixtures/comm/ab3.expected
new file mode 100644
index 000000000..1898bc804
--- /dev/null
+++ b/tests/fixtures/comm/ab3.expected
@@ -0,0 +1,2 @@
+a
+	b
diff --git a/tests/fixtures/comm/aempty.expected b/tests/fixtures/comm/aempty.expected
new file mode 100644
index 000000000..58f424cdb
--- /dev/null
+++ b/tests/fixtures/comm/aempty.expected
@@ -0,0 +1,2 @@
+a
+z
diff --git a/tests/fixtures/comm/b b/tests/fixtures/comm/b
new file mode 100644
index 000000000..63d7d7058
--- /dev/null
+++ b/tests/fixtures/comm/b
@@ -0,0 +1,2 @@
+b
+z
diff --git a/tests/fixtures/comm/empty b/tests/fixtures/comm/empty
new file mode 100644
index 000000000..e69de29bb
diff --git a/tests/fixtures/comm/emptyempty.expected b/tests/fixtures/comm/emptyempty.expected
new file mode 100644
index 000000000..e69de29bb