diff --git a/Cargo.toml b/Cargo.toml
index e00ba93..adf0f67 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -35,8 +35,8 @@ serde = { version = "1", features = ["derive"] }
 serde_json = { version = "1", features = ["float_roundtrip"] }
 log = "0.4"
 
-# 3MF packages (docs/formats/tagged-mesh.md).
-zip = { version = "3", default-features = false, features = ["deflate"] }
+# 3MF packages (docs/formats/tagged-mesh.md). zip is ahead of SolidCraft (still on 3), so both are built.
+zip = { version = "9", default-features = false, features = ["deflate"] }
 quick-xml = "0.42"
 
 # content hashes and part checksums of .fieldcraft files (the version SolidCraft uses)
diff --git a/crates/geometry/src/tagged_mesh.rs b/crates/geometry/src/tagged_mesh.rs
index 98a4f5a..20e1b89 100644
--- a/crates/geometry/src/tagged_mesh.rs
+++ b/crates/geometry/src/tagged_mesh.rs
@@ -446,7 +446,7 @@ mod tests {
         for (name, data) in [("[Content_Types].xml", types), ("_rels/.rels", rels), ("3D/3dmodel.model", x.as_str())] {
             let o = zip::write::SimpleFileOptions::default()
                 .compression_method(zip::CompressionMethod::Deflated)
-                .last_modified_time(zip::DateTime::default());
+                .last_modified_time(Some(zip::DateTime::default()));
             zip.start_file(name, o).unwrap();
             zip.write_all(data.as_bytes()).unwrap();
         }
diff --git a/crates/io/src/lib.rs b/crates/io/src/lib.rs
index fdee8c7..044bb94 100644
--- a/crates/io/src/lib.rs
+++ b/crates/io/src/lib.rs
@@ -335,7 +335,7 @@ pub fn write(model: &Model, geometry: &Geometry, journal: &[JournalEntry], view:
         // Fixed time and permissions: the bytes depend on the model only.
         let options = zip::write::SimpleFileOptions::default()
             .compression_method(zip::CompressionMethod::Stored)
-            .last_modified_time(zip::DateTime::default())
+            .last_modified_time(Some(zip::DateTime::default()))
             .unix_permissions(0o644)
             .large_file(bytes.len() as u64 >= u64::from(u32::MAX));
         zip.start_file(name, options).map_err(zip_error)?;