diff --git a/src/con_duct/__main__.py b/src/con_duct/__main__.py
index 211ccf2b..34bddd3a 100644
--- a/src/con_duct/__main__.py
+++ b/src/con_duct/__main__.py
@@ -169,9 +169,7 @@ class Averages:
     num_samples: int = 0
 
     def update(self: Averages, other: Sample) -> None:
-        assert_num(
-            other.total_rss, other.total_vsz, other.total_pmem, other.total_pcpu
-        )
+        assert_num(other.total_rss, other.total_vsz, other.total_pmem, other.total_pcpu)
         self.num_samples += 1
         self.rss += (other.total_rss - self.rss) / self.num_samples
         self.vsz += (other.total_vsz - self.vsz) / self.num_samples
@@ -330,7 +328,9 @@ def collect_sample(self) -> Sample:
             )
             for line in output.splitlines()[1:]:
                 if line:
-                    pid, pcpu, pmem, rss_kib, vsz_kib, etime, cmd = line.split(maxsplit=6)
+                    pid, pcpu, pmem, rss_kib, vsz_kib, etime, cmd = line.split(
+                        maxsplit=6
+                    )
                     sample.add_pid(
                         int(pid),
                         ProcessStats(
@@ -401,8 +401,9 @@ def dump_json(self) -> str:
             }
         )
 
-    def print_summary(self) -> None:
-        print(self.summary_format.format_map(self.execution_summary))
+    @cached_property
+    def execution_summary_formatted(self) -> str:
+        return self.summary_format.format_map(self.execution_summary)
 
 
 @dataclass
@@ -471,7 +472,7 @@ def from_argv(cls) -> Arguments:  # pragma: no cover
             "-q",
             "--quiet",
             action="store_true",
-            help="Suppress duct output.",
+            help="Suppress duct output of summary (to stderr).",
         )
         parser.add_argument(
             "--sample-interval",
@@ -647,6 +648,10 @@ def safe_close_files(file_list: Iterable[Any]) -> None:
             pass
 
 
+def duct_print(msg: str) -> None:
+    print(msg, file=sys.stderr)
+
+
 def main() -> None:
     args = Arguments.from_argv()
     sys.exit(execute(args))
@@ -673,8 +678,8 @@ def execute(args: Arguments) -> int:
 
     full_command = " ".join([str(args.command)] + args.command_args)
     if not args.quiet:
-        print(f"duct is executing {full_command}...")
-        print(f"Log files will be written to {log_paths.prefix}")
+        duct_print(f"duct is executing {full_command}...")
+        duct_print(f"Log files will be written to {log_paths.prefix}")
     process = subprocess.Popen(
         [str(args.command)] + args.command_args,
         stdout=stdout_file,
@@ -730,7 +735,7 @@ def execute(args: Arguments) -> int:
             report.get_system_info()
             system_logs.write(report.dump_json())
     if not args.quiet:
-        report.print_summary()
+        duct_print(report.execution_summary_formatted)
     safe_close_files([stdout_file, stdout, stderr_file, stderr])
 
     return report.process.returncode
diff --git a/test/test_execution.py b/test/test_execution.py
index 4bd3ca4f..a2c34dc5 100644
--- a/test/test_execution.py
+++ b/test/test_execution.py
@@ -55,9 +55,9 @@ def test_sanity_red(exit_code: int, temp_output_dir: str) -> None:
         summary_format=EXECUTION_SUMMARY_FORMAT,
         quiet=False,
     )
-    with mock.patch("sys.stdout", new_callable=mock.MagicMock) as mock_stdout:
+    with mock.patch("sys.stderr", new_callable=mock.MagicMock) as mock_stderr:
         assert execute(args) == exit_code
-        call_args = [call.args for call in mock_stdout.write.call_args_list]
+        call_args = [call.args for call in mock_stderr.write.call_args_list]
         assert any(f"Exit Code: {exit_code}" in call_arg[0] for call_arg in call_args)
 
     # We still should execute normally
@@ -179,9 +179,9 @@ def test_outputs_none_quiet(temp_output_dir: str) -> None:
         summary_format="",
         quiet=True,
     )
-    with mock.patch("sys.stdout", new_callable=mock.MagicMock) as mock_stdout:
+    with mock.patch("sys.stderr", new_callable=mock.MagicMock) as mock_stderr:
         assert execute(args) == 0
-        mock_stdout.write.assert_not_called()
+        mock_stderr.write.assert_not_called()
 
 
 def test_exit_before_first_sample(temp_output_dir: str) -> None: