diff --git a/listings/ch11-writing-automated-tests/listing-11-03/src/lib.rs b/listings/ch11-writing-automated-tests/listing-11-03/src/lib.rs
index 866f0238ba..336ea081a1 100644
--- a/listings/ch11-writing-automated-tests/listing-11-03/src/lib.rs
+++ b/listings/ch11-writing-automated-tests/listing-11-03/src/lib.rs
@@ -1,4 +1,4 @@
-pub fn add(left: usize, right: usize) -> usize {
+pub fn add(left: u64, right: u64) -> u64 {
     left + right
 }
 
diff --git a/listings/ch11-writing-automated-tests/no-listing-01-changing-test-name/src/lib.rs b/listings/ch11-writing-automated-tests/no-listing-01-changing-test-name/src/lib.rs
index 5be58b93fc..5014a76f2b 100644
--- a/listings/ch11-writing-automated-tests/no-listing-01-changing-test-name/src/lib.rs
+++ b/listings/ch11-writing-automated-tests/no-listing-01-changing-test-name/src/lib.rs
@@ -1,4 +1,4 @@
-pub fn add(left: usize, right: usize) -> usize {
+pub fn add(left: u64, right: u64) -> u64 {
     left + right
 }
 
diff --git a/listings/ch11-writing-automated-tests/no-listing-10-result-in-tests/src/lib.rs b/listings/ch11-writing-automated-tests/no-listing-10-result-in-tests/src/lib.rs
index c31cdcae45..06b1a03e1f 100644
--- a/listings/ch11-writing-automated-tests/no-listing-10-result-in-tests/src/lib.rs
+++ b/listings/ch11-writing-automated-tests/no-listing-10-result-in-tests/src/lib.rs
@@ -1,4 +1,4 @@
-pub fn add(left: usize, right: usize) -> usize {
+pub fn add(left: u64, right: u64) -> u64 {
     left + right
 }
 
diff --git a/listings/ch11-writing-automated-tests/no-listing-11-ignore-a-test/src/lib.rs b/listings/ch11-writing-automated-tests/no-listing-11-ignore-a-test/src/lib.rs
index 0c8b38defd..05fbe1af0a 100644
--- a/listings/ch11-writing-automated-tests/no-listing-11-ignore-a-test/src/lib.rs
+++ b/listings/ch11-writing-automated-tests/no-listing-11-ignore-a-test/src/lib.rs
@@ -1,4 +1,4 @@
-pub fn add(left: usize, right: usize) -> usize {
+pub fn add(left: u64, right: u64) -> u64 {
     left + right
 }
 
diff --git a/src/ch11-01-writing-tests.md b/src/ch11-01-writing-tests.md
index 93009f4d09..b04f0c2fee 100644
--- a/src/ch11-01-writing-tests.md
+++ b/src/ch11-01-writing-tests.md
@@ -62,6 +62,9 @@ cd ../../..
 
 </Listing>
 
+The file starts with an example `add` function, so that we have something
+to test.
+
 For now, let’s focus solely on the `it_works` function. Note the `#[test]`
 annotation: this attribute indicates this is a test function, so the test
 runner knows to treat this function as a test. We might also have non-test
@@ -69,9 +72,9 @@ functions in the `tests` module to help set up common scenarios or perform
 common operations, so we always need to indicate which functions are tests.
 
 The example function body uses the `assert_eq!` macro to assert that `result`,
-which contains the result of adding 2 and 2, equals 4. This assertion serves as
-an example of the format for a typical test. Let’s run it to see that this test
-passes.
+which contains the result of calling `add` with 2 and 2, equals 4. This
+assertion serves as an example of the format for a typical test. Let’s run it
+to see that this test passes.
 
 The `cargo test` command runs all tests in our project, as shown in Listing
 11-2.