diff --git a/book/pom.xml b/book/pom.xml
index bade9d11..8a9b0c92 100644
--- a/book/pom.xml
+++ b/book/pom.xml
@@ -33,6 +33,8 @@ along with aoserv-daemon.  If not, see <https://www.gnu.org/licenses/>.
   <packaging>jar</packaging>
 
   <properties>
+    <!-- Must be set to ${git.commit.time} for snapshots or ISO 8601 timestamp for releases. -->
+    <project.build.outputTimestamp>${git.commit.time}</project.build.outputTimestamp>
     <module.name>com.aoindustries.aoserv.daemon.book</module.name>
     <!-- These values are copied from the project being documented -->
     <documented.artifactId>aoserv-daemon</documented.artifactId>
diff --git a/pom.xml b/pom.xml
index d54ac664..1f755667 100644
--- a/pom.xml
+++ b/pom.xml
@@ -33,6 +33,8 @@ along with aoserv-daemon.  If not, see <https://www.gnu.org/licenses/>.
   <packaging>jar</packaging>
 
   <properties>
+    <!-- Must be set to ${git.commit.time} for snapshots or ISO 8601 timestamp for releases. -->
+    <project.build.outputTimestamp>${git.commit.time}</project.build.outputTimestamp>
     <module.name>com.aoindustries.aoserv.daemon</module.name>
     <!-- TODO: Java 11 once CentOS 5 is gone -->
     <!-- Java 1.8 -->