diff --git a/docs/bundle.markdown b/docs/bundle.markdown
index 7b08afeb..848d10ab 100644
--- a/docs/bundle.markdown
+++ b/docs/bundle.markdown
@@ -8,6 +8,7 @@ jsonschema bundle <schema.json|.yaml>
   [--resolve/-r <schemas-or-directories> ...]
   [--extension/-e <extension>] [--ignore/-i <schemas-or-directories>]
   [--without-id/-w] [--default-dialect/-d <uri>] [--json/-j]
+  [--indentation/-n <spaces>]
   [--configuration/-C <path>] [--color auto|always|never]
 ```
 
@@ -25,6 +26,9 @@ to resolve remote references in advance and inline them into the given schema
 for local consumption or further distribution.  The JSON Schema CLI supports
 this functionality through the `bundle` command.
 
+Use `--indentation/-n` to set how many spaces each level of nesting of the
+result is laid out with, which defaults to two.
+
 > [!WARNING]
 > A popular use case for JSON Schema is providing auto-completion for code
 > editors. If you plan to use your bundled schema for this, keep in mind that
diff --git a/docs/upgrade.markdown b/docs/upgrade.markdown
index 42024ffa..493a7f82 100644
--- a/docs/upgrade.markdown
+++ b/docs/upgrade.markdown
@@ -7,7 +7,7 @@ jsonschema upgrade <schema.json|.yaml> [--to/-t draft4|draft6|draft7|2019-09|202
   [--header/-H "<name>: <value>"]
   [--resolve/-r <schemas-or-directories> ...]
   [--default-dialect/-d <uri>] [--configuration/-C <path>]
-  [--color auto|always|never]
+  [--indentation/-n <spaces>] [--color auto|always|never]
 ```
 
 > [!NOTE]
@@ -21,6 +21,9 @@ specifications into account, including re-writing references that point at
 locations whose path has changed. By default, schemas are upgraded to the
 latest supported dialect, and the result is printed to standard output.
 
+Use `--indentation/-n` to set how many spaces each level of nesting of the
+result is laid out with, which defaults to two.
+
 For example, consider the following Draft 3 schema:
 
 ```json
diff --git a/src/command_bundle.cc b/src/command_bundle.cc
index 17a9ff2e..7a259378 100644
--- a/src/command_bundle.cc
+++ b/src/command_bundle.cc
@@ -22,6 +22,7 @@ auto sourcemeta::jsonschema::bundle(const sourcemeta::core::Options &options)
   }
 
   validate_http_headers(options);
+  const auto indentation{parse_indentation(options)};
 
   const std::filesystem::path schema_path{options.positional().front()};
   const bool schema_from_stdin = (schema_path == "-");
@@ -118,6 +119,6 @@ auto sourcemeta::jsonschema::bundle(const sourcemeta::core::Options &options)
         schema_display_path, error.what());
   }
 
-  sourcemeta::core::prettify(schema, std::cout);
+  sourcemeta::core::prettify(schema, std::cout, indentation);
   std::cout << "\n";
 }
diff --git a/src/command_upgrade.cc b/src/command_upgrade.cc
index 29bf6aac..9ff2d94c 100644
--- a/src/command_upgrade.cc
+++ b/src/command_upgrade.cc
@@ -159,6 +159,7 @@ auto sourcemeta::jsonschema::upgrade(const sourcemeta::core::Options &options)
   const auto target_value{options.contains("to") ? options.at("to").front()
                                                  : std::string_view{"2020-12"}};
   const auto target_dialect{parse_target_dialect(target_value)};
+  const auto indentation{parse_indentation(options)};
 
   const std::filesystem::path schema_path{options.positional().front()};
   const bool schema_from_stdin = (schema_path == "-");
@@ -197,6 +198,6 @@ auto sourcemeta::jsonschema::upgrade(const sourcemeta::core::Options &options)
 
   sourcemeta::jsonschema::format_schema(schema, custom_resolver, dialect);
 
-  sourcemeta::core::prettify(schema, std::cout);
+  sourcemeta::core::prettify(schema, std::cout, indentation);
   std::cout << "\n";
 }
diff --git a/src/error.h b/src/error.h
index 4c736fb3..4f6848ee 100644
--- a/src/error.h
+++ b/src/error.h
@@ -216,6 +216,13 @@ class InvalidJobsError : public std::runtime_error {
       : std::runtime_error{"The --jobs option must be a positive integer"} {}
 };
 
+class InvalidIndentationError : public std::runtime_error {
+public:
+  InvalidIndentationError()
+      : std::runtime_error{
+            "The --indentation option must be a non-negative integer"} {}
+};
+
 class InvalidLintRuleError : public std::runtime_error {
 public:
   InvalidLintRuleError(const std::string &message, std::string rule)
@@ -1652,6 +1659,10 @@ inline auto try_catch(const sourcemeta::core::Options &options,
     const auto is_json{options.contains("json")};
     print_exception(is_json, error);
     return EXIT_INVALID_CLI_ARGUMENTS;
+  } catch (const InvalidIndentationError &error) {
+    const auto is_json{options.contains("json")};
+    print_exception(is_json, error);
+    return EXIT_INVALID_CLI_ARGUMENTS;
   } catch (const InvalidOptionEnumerationValueError &error) {
     const auto is_json{options.contains("json")};
     print_exception(is_json, error);
diff --git a/src/main.cc b/src/main.cc
index ccef365a..017fc03d 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -117,6 +117,7 @@ constexpr std::string_view USAGE_COMMANDS{R"EOF(   version / --version / -v
 
    upgrade <schema.json|.yaml>
            [--to/-t draft4|draft6|draft7|2019-09|2020-12]
+           [--indentation/-n <spaces>]
 
        Upgrade the given schema to a newer JSON Schema dialect.
        Defaults to the latest dialect (2020-12). Schemas that declare a
@@ -125,6 +126,7 @@ constexpr std::string_view USAGE_COMMANDS{R"EOF(   version / --version / -v
 
    bundle <schema.json|.yaml> [--extension/-e <extension>]
           [--ignore/-i <schemas-or-directories>] [--without-id/-w]
+          [--indentation/-n <spaces>]
 
        Perform JSON Schema Bundling on a schema to inline remote references,
        printing the result to standard output.
@@ -283,6 +285,7 @@ auto jsonschema_main(const std::string &program, const std::string &command,
     app.flag("without-id", {"w"});
     app.option("extension", {"e"});
     app.option("ignore", {"i"});
+    app.option("indentation", {"n"});
     parse_options(app, argc, argv, {.skip = 1});
     sourcemeta::jsonschema::bundle(app);
     return EXIT_SUCCESS;
@@ -387,6 +390,7 @@ auto jsonschema_main(const std::string &program, const std::string &command,
 
   if (command == "upgrade") {
     app.option("to", {"t"});
+    app.option("indentation", {"n"});
     parse_options(app, argc, argv, {.skip = 1});
     sourcemeta::jsonschema::upgrade(app);
     return EXIT_SUCCESS;
diff --git a/src/utils.h b/src/utils.h
index 3eed8538..a00cd922 100644
--- a/src/utils.h
+++ b/src/utils.h
@@ -228,11 +228,22 @@ inline auto parse_jobs(const sourcemeta::core::Options &options)
 
 inline auto parse_indentation(const sourcemeta::core::Options &options)
     -> std::size_t {
-  if (options.contains("indentation")) {
-    return std::stoull(std::string{options.at("indentation").front()});
+  if (!options.contains("indentation")) {
+    return 2;
   }
 
-  return 2;
+  const std::string value{options.at("indentation").front()};
+  if (value.empty() || !std::ranges::all_of(value, [](const char character) {
+        return std::isdigit(static_cast<unsigned char>(character));
+      })) {
+    throw InvalidIndentationError{};
+  }
+
+  try {
+    return std::stoull(value);
+  } catch (const std::out_of_range &) {
+    throw InvalidIndentationError{};
+  }
 }
 
 inline auto format_assertion_tweaks(const sourcemeta::core::Options &options)
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 27fed952..5ccbe85e 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -72,6 +72,7 @@ add_jsonschema_test(format/pass_yaml_anchor_without_alias)
 add_jsonschema_test(format/pass_yaml_anchors_keep_ordering)
 add_jsonschema_test(format/pass_yaml_keep_ordering)
 add_jsonschema_test(format/pass_yaml_indentation)
+add_jsonschema_test(format/fail_invalid_indentation)
 add_jsonschema_test(format/pass_yaml_intact_mtime)
 add_jsonschema_test(format/pass_yaml_stdin)
 add_jsonschema_test(format/pass_yaml_directory)
@@ -682,6 +683,8 @@ add_jsonschema_test(bundle/pass_2020_12_http)
 add_jsonschema_test(bundle/pass_resolve_single_default_dialect)
 add_jsonschema_test(bundle/pass_boolean_schema_default_dialect)
 add_jsonschema_test(bundle/pass_resolve_yaml)
+add_jsonschema_test(bundle/pass_indentation)
+add_jsonschema_test(bundle/fail_invalid_indentation)
 add_jsonschema_test(bundle/pass_resolve_with_ignore)
 add_jsonschema_test(bundle/pass_resolve_no_identifier)
 add_jsonschema_test(bundle/pass_without_id)
@@ -874,6 +877,7 @@ add_jsonschema_test(lint/fail_lint_openapi_version)
 add_jsonschema_test(lint/fail_lint_openapi_version_newer)
 add_jsonschema_test(lint/fail_lint_openapi_version_malformed)
 add_jsonschema_test(lint/fail_lint_openapi_version_not_a_string)
+add_jsonschema_test(lint/fail_lint_invalid_indentation)
 add_jsonschema_test(lint/fail_lint)
 add_jsonschema_test(lint/fail_lint_color_always)
 add_jsonschema_test(lint/fail_lint_color_never)
@@ -1209,6 +1213,8 @@ add_jsonschema_test(upgrade/pass_default_dialect)
 add_jsonschema_test(upgrade/pass_configuration_option)
 add_jsonschema_test(upgrade/pass_resolve)
 add_jsonschema_test(upgrade/pass_yaml_input)
+add_jsonschema_test(upgrade/pass_indentation)
+add_jsonschema_test(upgrade/fail_invalid_indentation)
 add_jsonschema_test(upgrade/pass_embedded_resources)
 add_jsonschema_test(upgrade/fail_custom_metaschema_root)
 add_jsonschema_test(upgrade/fail_custom_metaschema_nested)
diff --git a/test/bundle/fail_invalid_indentation.clitest b/test/bundle/fail_invalid_indentation.clitest
new file mode 100644
index 00000000..d2a76a56
--- /dev/null
+++ b/test/bundle/fail_invalid_indentation.clitest
@@ -0,0 +1,27 @@
+WRITE schema.json UNTIL EOF
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://example.com",
+  "$ref": "nested"
+}
+EOF
+
+// Invalid CLI arguments
+RUN bundle schema.json --indentation abc STDIN /dev/null IN . INTO result_0.txt EXPECTING 5
+
+WRITE expected_0.txt UNTIL EOF
+2> error: The --indentation option must be a non-negative integer
+EOF
+
+COMPARE result_0.txt AGAINST expected_0.txt
+
+// Invalid CLI arguments
+RUN bundle schema.json --indentation abc --json STDIN /dev/null IN . INTO result_1.txt EXPECTING 5
+
+WRITE expected_1.txt UNTIL EOF
+1> {
+1>   "error": "The --indentation option must be a non-negative integer"
+1> }
+EOF
+
+COMPARE result_1.txt AGAINST expected_1.txt
diff --git a/test/bundle/pass_indentation.clitest b/test/bundle/pass_indentation.clitest
new file mode 100644
index 00000000..c7274379
--- /dev/null
+++ b/test/bundle/pass_indentation.clitest
@@ -0,0 +1,34 @@
+WRITE schema.json UNTIL EOF
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://example.com",
+  "$ref": "nested"
+}
+EOF
+
+WRITE remote.json UNTIL EOF
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://example.com/nested",
+  "type": "string"
+}
+EOF
+
+RUN bundle schema.json --resolve remote.json --indentation 4 STDIN /dev/null IN . INTO result.txt EXPECTING 0
+
+WRITE expected.txt UNTIL EOF
+1> {
+1>     "$schema": "https://json-schema.org/draft/2020-12/schema",
+1>     "$id": "https://example.com",
+1>     "$ref": "nested",
+1>     "$defs": {
+1>         "https://example.com/nested": {
+1>             "$schema": "https://json-schema.org/draft/2020-12/schema",
+1>             "$id": "https://example.com/nested",
+1>             "type": "string"
+1>         }
+1>     }
+1> }
+EOF
+
+COMPARE result.txt AGAINST expected.txt
diff --git a/test/format/fail_invalid_indentation.clitest b/test/format/fail_invalid_indentation.clitest
new file mode 100644
index 00000000..7985db6a
--- /dev/null
+++ b/test/format/fail_invalid_indentation.clitest
@@ -0,0 +1,26 @@
+WRITE schema.json UNTIL EOF
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "type": "string"
+}
+EOF
+
+// Invalid CLI arguments
+RUN fmt schema.json --indentation abc STDIN /dev/null IN . INTO result_0.txt EXPECTING 5
+
+WRITE expected_0.txt UNTIL EOF
+2> error: The --indentation option must be a non-negative integer
+EOF
+
+COMPARE result_0.txt AGAINST expected_0.txt
+
+// Invalid CLI arguments
+RUN fmt schema.json --indentation abc --json STDIN /dev/null IN . INTO result_1.txt EXPECTING 5
+
+WRITE expected_1.txt UNTIL EOF
+1> {
+1>   "error": "The --indentation option must be a non-negative integer"
+1> }
+EOF
+
+COMPARE result_1.txt AGAINST expected_1.txt
diff --git a/test/help_command.clitest b/test/help_command.clitest
index f0f9fb24..5483e098 100644
--- a/test/help_command.clitest
+++ b/test/help_command.clitest
@@ -127,6 +127,7 @@ WRITE expected.txt UNTIL EOF
 1>
 1>    upgrade <schema.json|.yaml>
 1>            [--to/-t draft4|draft6|draft7|2019-09|2020-12]
+1>            [--indentation/-n <spaces>]
 1>
 1>        Upgrade the given schema to a newer JSON Schema dialect.
 1>        Defaults to the latest dialect (2020-12). Schemas that declare a
@@ -135,6 +136,7 @@ WRITE expected.txt UNTIL EOF
 1>
 1>    bundle <schema.json|.yaml> [--extension/-e <extension>]
 1>           [--ignore/-i <schemas-or-directories>] [--without-id/-w]
+1>           [--indentation/-n <spaces>]
 1>
 1>        Perform JSON Schema Bundling on a schema to inline remote references,
 1>        printing the result to standard output.
diff --git a/test/help_option_long.clitest b/test/help_option_long.clitest
index 151185bd..a92e348a 100644
--- a/test/help_option_long.clitest
+++ b/test/help_option_long.clitest
@@ -118,6 +118,7 @@ WRITE expected.txt UNTIL EOF
 1>
 1>    [ANSI_BOLD_CYAN]upgrade[ANSI_RESET] <schema.json|.yaml>
 1>            [--to/-t draft4|draft6|draft7|2019-09|2020-12]
+1>            [--indentation/-n <spaces>]
 1>
 1>        Upgrade the given schema to a newer JSON Schema dialect.
 1>        Defaults to the latest dialect (2020-12). Schemas that declare a
@@ -126,6 +127,7 @@ WRITE expected.txt UNTIL EOF
 1>
 1>    [ANSI_BOLD_CYAN]bundle[ANSI_RESET] <schema.json|.yaml> [--extension/-e <extension>]
 1>           [--ignore/-i <schemas-or-directories>] [--without-id/-w]
+1>           [--indentation/-n <spaces>]
 1>
 1>        Perform JSON Schema Bundling on a schema to inline remote references,
 1>        printing the result to standard output.
diff --git a/test/help_option_short.clitest b/test/help_option_short.clitest
index 65962342..f2fcbcb0 100644
--- a/test/help_option_short.clitest
+++ b/test/help_option_short.clitest
@@ -115,6 +115,7 @@ WRITE expected.txt UNTIL EOF
 1>
 1>    upgrade <schema.json|.yaml>
 1>            [--to/-t draft4|draft6|draft7|2019-09|2020-12]
+1>            [--indentation/-n <spaces>]
 1>
 1>        Upgrade the given schema to a newer JSON Schema dialect.
 1>        Defaults to the latest dialect (2020-12). Schemas that declare a
@@ -123,6 +124,7 @@ WRITE expected.txt UNTIL EOF
 1>
 1>    bundle <schema.json|.yaml> [--extension/-e <extension>]
 1>           [--ignore/-i <schemas-or-directories>] [--without-id/-w]
+1>           [--indentation/-n <spaces>]
 1>
 1>        Perform JSON Schema Bundling on a schema to inline remote references,
 1>        printing the result to standard output.
diff --git a/test/lint/fail_lint_invalid_indentation.clitest b/test/lint/fail_lint_invalid_indentation.clitest
new file mode 100644
index 00000000..4c2785c0
--- /dev/null
+++ b/test/lint/fail_lint_invalid_indentation.clitest
@@ -0,0 +1,26 @@
+WRITE schema.json UNTIL EOF
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "type": "string"
+}
+EOF
+
+// Invalid CLI arguments
+RUN lint schema.json --indentation abc STDIN /dev/null IN . INTO result_0.txt EXPECTING 5
+
+WRITE expected_0.txt UNTIL EOF
+2> error: The --indentation option must be a non-negative integer
+EOF
+
+COMPARE result_0.txt AGAINST expected_0.txt
+
+// Invalid CLI arguments
+RUN lint schema.json --indentation abc --json STDIN /dev/null IN . INTO result_1.txt EXPECTING 5
+
+WRITE expected_1.txt UNTIL EOF
+1> {
+1>   "error": "The --indentation option must be a non-negative integer"
+1> }
+EOF
+
+COMPARE result_1.txt AGAINST expected_1.txt
diff --git a/test/upgrade/fail_invalid_indentation.clitest b/test/upgrade/fail_invalid_indentation.clitest
new file mode 100644
index 00000000..bdfc5405
--- /dev/null
+++ b/test/upgrade/fail_invalid_indentation.clitest
@@ -0,0 +1,26 @@
+WRITE schema.json UNTIL EOF
+{
+  "$schema": "http://json-schema.org/draft-04/schema#",
+  "type": "string"
+}
+EOF
+
+// Invalid CLI arguments
+RUN upgrade schema.json --indentation abc STDIN /dev/null IN . INTO result_0.txt EXPECTING 5
+
+WRITE expected_0.txt UNTIL EOF
+2> error: The --indentation option must be a non-negative integer
+EOF
+
+COMPARE result_0.txt AGAINST expected_0.txt
+
+// Invalid CLI arguments
+RUN upgrade schema.json --indentation abc --json STDIN /dev/null IN . INTO result_1.txt EXPECTING 5
+
+WRITE expected_1.txt UNTIL EOF
+1> {
+1>   "error": "The --indentation option must be a non-negative integer"
+1> }
+EOF
+
+COMPARE result_1.txt AGAINST expected_1.txt
diff --git a/test/upgrade/pass_indentation.clitest b/test/upgrade/pass_indentation.clitest
new file mode 100644
index 00000000..d4797d5e
--- /dev/null
+++ b/test/upgrade/pass_indentation.clitest
@@ -0,0 +1,25 @@
+WRITE schema.json UNTIL EOF
+{
+  "$schema": "http://json-schema.org/draft-04/schema#",
+  "id": "https://example.com/test",
+  "properties": {
+    "foo": { "type": "string" }
+  }
+}
+EOF
+
+RUN upgrade schema.json --indentation 4 STDIN /dev/null IN . INTO result.txt EXPECTING 0
+
+WRITE expected.txt UNTIL EOF
+1> {
+1>     "$schema": "https://json-schema.org/draft/2020-12/schema",
+1>     "$id": "https://example.com/test",
+1>     "properties": {
+1>         "foo": {
+1>             "type": "string"
+1>         }
+1>     }
+1> }
+EOF
+
+COMPARE result.txt AGAINST expected.txt