diff --git a/README.md b/README.md
index f6bb396..13b34d4 100644
--- a/README.md
+++ b/README.md
@@ -68,7 +68,7 @@ Tight packing places some constraints on the underlying data:
 - Maximum database size: 4GB.
 - Permitted length of username and groupname: 1-32 bytes.
 - Permitted length of shell and home: 1-64 bytes.
-- Permitted comment ("gecos") length: 0-255 bytes.
+- Permitted comment ("gecos") length: 0-1023 bytes.
 - User name, groupname and gecos must be utf8-encoded.
 
 Checking out and building
diff --git a/src/user.zig b/src/user.zig
index de90a64..d55687c 100644
--- a/src/user.zig
+++ b/src/user.zig
@@ -14,8 +14,8 @@ pub const PackedUser = packed struct {
     home_len: u6,
     name_is_a_suffix: bool,
     name_len: u5,
-    gecos_len: u8,
-    padding: u5,
+    gecos_len: u10,
+    padding: u3,
 
     // blobSize returns the length of the blob storing string values.
     pub fn blobLength(self: *const PackedUser) usize {
@@ -88,7 +88,7 @@ pub const UserWriter = struct {
         const home_len = try downCast(u6, user.home.len - 1);
         const name_len = try downCast(u5, user.name.len - 1);
         const shell_len = try downCast(u6, user.shell.len - 1);
-        const gecos_len = try downCast(u8, user.gecos.len);
+        const gecos_len = try downCast(u10, user.gecos.len);
 
         var puser = PackedUser{
             .uid = user.uid,
@@ -259,7 +259,7 @@ test "construct PackedUser blob" {
         .uid = 0,
         .gid = 4294967295,
         .name = "n" ** 32,
-        .gecos = "g" ** 255,
+        .gecos = "g" ** 1023,
         .home = "h" ** 64,
         .shell = "s" ** 64,
     } };