diff --git a/src/sections.zig b/src/sections.zig
index f0a9209..59ca6c0 100644
--- a/src/sections.zig
+++ b/src/sections.zig
@@ -394,10 +394,16 @@ fn cmpGroup(_: void, a: Group, b: Group) bool {
 }
 
 // nblocks returns how many blocks a particular slice will take.
-fn nblocks(arr: []const u8) u32 {
-    const upper = pad.roundUp(u38, section_length_bits, @intCast(u38, arr.len));
+fn nblocks(comptime T: type, arr: []const u8) T {
+    const B = switch (T) {
+        u8 => u14,
+        u32 => u38,
+        u64 => u70,
+        else => @compileError("only u8, u32 and u64 are supported"),
+    };
+    const upper = pad.roundUp(B, section_length_bits, @intCast(B, arr.len));
     assert(upper & (section_length - 1) == 0);
-    return @truncate(u32, upper >> 6);
+    return @truncate(T, upper >> 6);
 }
 
 pub const AllSections = struct {
@@ -780,8 +786,12 @@ test "nblocks" {
         .{ 1, &[_]u8{1} ** 63 },
         .{ 1, &[_]u8{1} ** 64 },
         .{ 2, &[_]u8{1} ** 65 },
+        .{ 255, &[_]u8{1} ** (255 * 64) },
     };
 
-    inline for (tests) |tt|
-        try testing.expectEqual(@as(u32, tt[0]), nblocks(tt[1]));
+    inline for (tests) |tt| {
+        try testing.expectEqual(nblocks(u8, tt[1]), tt[0]);
+        try testing.expectEqual(nblocks(u32, tt[1]), tt[0]);
+        try testing.expectEqual(nblocks(u64, tt[1]), tt[0]);
+    }
 }