diff --git a/listings/ch11-writing-automated-tests/listing-11-01/src/lib.rs b/listings/ch11-writing-automated-tests/listing-11-01/src/lib.rs
index 7d12d9af81..b93cf3ffd9 100644
--- a/listings/ch11-writing-automated-tests/listing-11-01/src/lib.rs
+++ b/listings/ch11-writing-automated-tests/listing-11-01/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/listing-11-03/src/lib.rs b/listings/ch11-writing-automated-tests/listing-11-03/src/lib.rs
index 67b6552c71..f83db0ed6d 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
@@ -1,5 +1,5 @@
 // ANCHOR: here
-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/ch14-more-about-cargo/output-only-02-add-one/add/add_one/src/lib.rs b/listings/ch14-more-about-cargo/output-only-02-add-one/add/add_one/src/lib.rs
index 7d12d9af81..b93cf3ffd9 100644
--- a/listings/ch14-more-about-cargo/output-only-02-add-one/add/add_one/src/lib.rs
+++ b/listings/ch14-more-about-cargo/output-only-02-add-one/add/add_one/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
 }