diff --git a/src/librustc_errors/lib.rs b/src/librustc_errors/lib.rs
index 999c3470e71e..2279ed859540 100644
--- a/src/librustc_errors/lib.rs
+++ b/src/librustc_errors/lib.rs
@@ -746,7 +746,8 @@ impl HandlerInner {
             !this.emitted_diagnostics.insert(diagnostic_hash)
         };
 
-        // Only emit the diagnostic if we haven't already emitted an equivalent one.
+        // Only emit the diagnostic if we've been asked to deduplicate and
+        // haven't already emitted an equivalent diagnostic.
         if !(self.flags.deduplicate_diagnostics && already_emitted(self)) {
             self.emitter.emit_diagnostic(diagnostic);
             if diagnostic.is_error() {
diff --git a/src/librustdoc/core.rs b/src/librustdoc/core.rs
index c48523961de0..5f2ce34afeec 100644
--- a/src/librustdoc/core.rs
+++ b/src/librustdoc/core.rs
@@ -184,7 +184,7 @@ pub fn new_handler(
                     debugging_opts.terminal_width,
                     false,
                 )
-                .ui_testing(debugging_opts.ui_testing),
+                .ui_testing(debugging_opts.ui_testing()),
             )
         }
         ErrorOutputType::Json { pretty, json_rendered } => {
@@ -193,7 +193,7 @@ pub fn new_handler(
             });
             Box::new(
                 JsonEmitter::stderr(None, source_map, pretty, json_rendered, false)
-                    .ui_testing(debugging_opts.ui_testing),
+                    .ui_testing(debugging_opts.ui_testing()),
             )
         }
     };