diff --git a/lib/std/crypto/Certificate/Bundle.zig b/lib/std/crypto/Certificate/Bundle.zig
index 4177676d96..b30fa531ec 100644
--- a/lib/std/crypto/Certificate/Bundle.zig
+++ b/lib/std/crypto/Certificate/Bundle.zig
@@ -108,7 +108,7 @@ pub fn addCertsFromFile(
     const needed_capacity = std.math.cast(u32, decoded_size_upper_bound + size) orelse
         return error.CertificateAuthorityBundleTooBig;
     try cb.bytes.ensureUnusedCapacity(gpa, needed_capacity);
-    const end_reserved = cb.bytes.items.len + decoded_size_upper_bound;
+    const end_reserved = @intCast(u32, cb.bytes.items.len + decoded_size_upper_bound);
     const buffer = cb.bytes.allocatedSlice()[end_reserved..];
     const end_index = try file.readAll(buffer);
     const encoded_bytes = buffer[0..end_index];