diff --git a/src/fd.zig b/src/fd.zig
index d8b92cfe68..acceaaf7e6 100644
--- a/src/fd.zig
+++ b/src/fd.zig
@@ -303,10 +303,6 @@ pub const FDImpl = packed struct {
     }
 
     pub fn format(this: FDImpl, comptime fmt: []const u8, _: std.fmt.FormatOptions, writer: anytype) !void {
-        if (fmt.len != 0) {
-            @compileError("invalid format string for FDImpl.format. must be either '' or 'd'");
-        }
-
         if (!this.isValid()) {
             try writer.writeAll("[invalid_fd]");
             return;
@@ -317,6 +313,10 @@ pub const FDImpl = packed struct {
             return;
         }
 
+        if (fmt.len != 0) {
+            @compileError("invalid format string for FDImpl.format. must be either '' or 'd'");
+        }
+
         switch (env.os) {
             else => {
                 const fd = this.system();