diff --git a/tests/test_toolargparse.py b/tests/test_toolargparse.py
index 2bf7a809a..4c46fe4ac 100644
--- a/tests/test_toolargparse.py
+++ b/tests/test_toolargparse.py
@@ -308,3 +308,27 @@ def test_argparse_append_with_default(job_order: list[str], expected_values: lis
     cmd_line = vars(toolparser.parse_args(job_order))
     file_paths = list(cmd_line["file_paths"])
     assert expected_values == file_paths
+
+
+@pytest.mark.parametrize(
+    "cwl_file,expected_default",
+    [
+        ("tests/wf/779-boolean-default-false.cwl", False),
+        ("tests/wf/779-boolean-default-true.cwl", True),
+    ],
+)
+def test_boolean_with_default_not_required(cwl_file: str, expected_default: bool) -> None:
+    """A boolean input with a default value must not be a required CLI argument.
+
+    Regression test for https://github.com/common-workflow-language/cwltool/issues/779
+    where ``default: false`` was incorrectly treated as a required ``--a_bool`` flag.
+    """
+    loadingContext = LoadingContext()
+    tool = load_tool(get_data(cwl_file), loadingContext)
+    # input_required=True mirrors the default CLI behavior; the input must still be
+    # optional purely because it declares a default value.
+    toolparser = generate_parser(argparse.ArgumentParser(prog="test"), tool, {}, [], True)
+    # Parsing with no arguments must succeed (the flag is optional) and fall back
+    # to the declared default rather than erroring with "arguments are required".
+    cmd_line = vars(toolparser.parse_args([]))
+    assert cmd_line["a_bool"] == expected_default
diff --git a/tests/wf/779-boolean-default-false.cwl b/tests/wf/779-boolean-default-false.cwl
new file mode 100644
index 000000000..57ea0129f
--- /dev/null
+++ b/tests/wf/779-boolean-default-false.cwl
@@ -0,0 +1,13 @@
+#!/usr/bin/env cwl-runner
+# Regression fixture for https://github.com/common-workflow-language/cwltool/issues/779
+# A boolean input with `default: false` must NOT become a required CLI argument.
+cwlVersion: v1.2
+class: CommandLineTool
+inputs:
+  a_bool:
+    type: boolean
+    default: false
+    inputBinding:
+      prefix: --a_bool
+outputs: []
+baseCommand: echo
diff --git a/tests/wf/779-boolean-default-true.cwl b/tests/wf/779-boolean-default-true.cwl
new file mode 100644
index 000000000..89a4f9bb2
--- /dev/null
+++ b/tests/wf/779-boolean-default-true.cwl
@@ -0,0 +1,13 @@
+#!/usr/bin/env cwl-runner
+# Companion fixture for https://github.com/common-workflow-language/cwltool/issues/779
+# A boolean input with `default: true` must also NOT be a required CLI argument.
+cwlVersion: v1.2
+class: CommandLineTool
+inputs:
+  a_bool:
+    type: boolean
+    default: true
+    inputBinding:
+      prefix: --a_bool
+outputs: []
+baseCommand: echo