diff --git a/src/librustc_interface/util.rs b/src/librustc_interface/util.rs
index a86d3cc43948d..6ae5e94b11af3 100644
--- a/src/librustc_interface/util.rs
+++ b/src/librustc_interface/util.rs
@@ -642,14 +642,14 @@ pub fn build_output_filenames(
                 );
                 None
             } else {
+                if !sess.opts.cg.extra_filename.is_empty() {
+                    sess.warn("ignoring -C extra-filename flag due to -o flag");
+                }
                 Some(out_file.clone())
             };
             if *odir != None {
                 sess.warn("ignoring --out-dir flag due to -o flag");
             }
-            if !sess.opts.cg.extra_filename.is_empty() {
-                sess.warn("ignoring -C extra-filename flag due to -o flag");
-            }
 
             OutputFilenames {
                 out_directory: out_file.parent().unwrap_or_else(|| Path::new("")).to_path_buf(),