diff --git a/subprojects/nix-eval-jobs/src/eval-args.cc b/subprojects/nix-eval-jobs/src/eval-args.cc
index 0406d323f..3800e7fff 100644
--- a/subprojects/nix-eval-jobs/src/eval-args.cc
+++ b/subprojects/nix-eval-jobs/src/eval-args.cc
@@ -22,8 +22,7 @@ MyArgs::MyArgs(nix::AsyncIoRoot & aio) : MixCommonArgs("nix-eval-jobs"), aio_(ai
                 if (hiddenCategories.count(flag->category)) {
                     continue;
                 }
-                printf("  --%-20s %s\n", name.c_str(),
-                       flag->description.c_str());
+                std::cout << nix::fmt("  --%-20s %s\n", name, flag->description);
             }
             ::exit(0);
         }},
diff --git a/subprojects/nix-eval-jobs/src/worker.cc b/subprojects/nix-eval-jobs/src/worker.cc
index bdfab0db3..07588ae05 100644
--- a/subprojects/nix-eval-jobs/src/worker.cc
+++ b/subprojects/nix-eval-jobs/src/worker.cc
@@ -156,8 +156,7 @@ void worker(nix::ref<nix::eval_cache::CachingEvaluator> evaluator,
             break;
         }
         if (!s.starts_with("do ")) {
-            fprintf(stderr, "worker error: received invalid command '%s'\n",
-                    s.data());
+            std::cerr << "worker error: received invalid command '" << s << "'\n";
             abort();
         }
         auto path = nix::json::parse(s.substr(3));
@@ -230,13 +229,13 @@ void worker(nix::ref<nix::eval_cache::CachingEvaluator> evaluator,
             reply["error"] = nix::filterANSIEscapes(msg, true);
             // Don't forget to print it into the STDERR log, this is
             // what's shown in the Hydra UI.
-            fprintf(stderr, "%s\n", msg.c_str());
+            std::cerr << msg << "\n";
         } catch ( // NOLINT(lix-foreign-exceptions)
             const std::exception &e) { // FIXME: for some reason the catch block
                                        // above, doesn't trigger on macOS (?)
             auto msg = e.what();
             reply["error"] = nix::filterANSIEscapes(msg, true);
-            fprintf(stderr, "%s\n", msg);
+            std::cerr << msg << "\n";
         }
 
         if (tryWriteLine(to.get(), reply.dump()) < 0) {