diff --git a/UPGRADE.md b/UPGRADE.md
index b094d61..03cd1f7 100644
--- a/UPGRADE.md
+++ b/UPGRADE.md
@@ -54,6 +54,8 @@
    - `::isValueRequiresQuoting()`
 - `::fetchItems()` can now return an `iterable` instead of `array`
 - `::getItemName()` can now take `null` for an unknown number of items
+- Ensures that if an item is given, then the processing is done in the main
+  process. An item also cannot be passed to a child process (via the argument).
 
 
 ## New extension points
diff --git a/src/Input/ParallelizationInput.php b/src/Input/ParallelizationInput.php
index 25f20c5..760a1b9 100644
--- a/src/Input/ParallelizationInput.php
+++ b/src/Input/ParallelizationInput.php
@@ -19,9 +19,11 @@
 use Symfony\Component\Console\Input\InputOption;
 use Webmozart\Assert\Assert;
 use Webmozarts\Console\Parallelization\CpuCoreCounter;
+use function get_class;
 use function gettype;
 use function is_int;
 use function is_numeric;
+use function is_object;
 use function sprintf;
 
 final class ParallelizationInput
@@ -70,14 +72,23 @@ public static function fromInput(InputInterface $input): self
     {
         /** @var string|null $numberOfProcesses */
         $numberOfProcesses = $input->getOption(self::PROCESSES_OPTION);
-        /** @var string|null $item */
+        /** @var mixed|null $item */
         $item = $input->getArgument(self::ITEM_ARGUMENT);
+        $hasItem = null !== $item;
         /** @var bool $mainProcess */
         $mainProcess = $input->getOption(self::MAIN_PROCESS_OPTION);
         /** @var bool $isChild */
         $isChild = $input->getOption(self::CHILD_OPTION);
 
+        if ($hasItem) {
+            $item = self::validateItem($item);
+            // When there is a single item passed, we do not want to spawn
+            // child processes.
+            $mainProcess = true;
+        }
+
         if ($mainProcess) {
+            // TODO: add this to the logger
             $validatedNumberOfProcesses = 1;
         } else {
             $validatedNumberOfProcesses = null !== $numberOfProcesses
@@ -85,21 +96,6 @@ public static function fromInput(InputInterface $input): self
                 : static fn () => CpuCoreCounter::getNumberOfCpuCores();
         }
 
-        $hasItem = null !== $item;
-
-        if ($hasItem && !is_numeric($item)) {
-            // Safeguard in case an invalid type is accidentally passed in tests when invoking the
-            // command directly
-            Assert::string(
-                $item,
-                sprintf(
-                    'Invalid item type. Expected a string, got "%s".',
-                    // TODO: change to get_debug_type() once dropping PHP 7.4
-                    gettype($input),
-                ),
-            );
-        }
-
         if ($isChild) {
             Assert::false(
                 $hasItem,
@@ -113,7 +109,7 @@ public static function fromInput(InputInterface $input): self
         return new self(
             $mainProcess,
             $validatedNumberOfProcesses,
-            $hasItem ? (string) $item : null,
+            $hasItem ? $item : null,
             $isChild,
         );
     }
@@ -178,6 +174,29 @@ public function isChildProcess(): bool
         return $this->childProcess;
     }
 
+    /**
+     * @param mixed $item
+     */
+    private static function validateItem($item): string
+    {
+        if (is_numeric($item)) {
+            return (string) $item;
+        }
+
+        // Safeguard in case an invalid type is accidentally passed in tests when invoking the
+        // command directly
+        Assert::string(
+            $item,
+            sprintf(
+                'Invalid item type. Expected a string, got "%s".',
+                // TODO: use get_debug_type when dropping PHP 7.4 support
+                is_object($item) ? get_class($item) : gettype($item),
+            ),
+        );
+
+        return $item;
+    }
+
     /**
      * @return positive-int
      */
diff --git a/tests/Fixtures/Command/NoSubProcessCommand.php b/tests/Fixtures/Command/NoSubProcessCommand.php
index 8404642..7470ca5 100644
--- a/tests/Fixtures/Command/NoSubProcessCommand.php
+++ b/tests/Fixtures/Command/NoSubProcessCommand.php
@@ -91,7 +91,7 @@ protected function runSingleCommand(string $item, InputInterface $input, OutputI
 
     protected function getItemName(?int $count): string
     {
-        return 0 === $count ? 'item' : 'items';
+        return 1 === $count ? 'item' : 'items';
     }
 
     protected function createLogger(OutputInterface $output): Logger
diff --git a/tests/Input/ParallelizationInputTest.php b/tests/Input/ParallelizationInputTest.php
index 2f623b3..215c43c 100644
--- a/tests/Input/ParallelizationInputTest.php
+++ b/tests/Input/ParallelizationInputTest.php
@@ -112,7 +112,7 @@ public function test_it_can_be_instantiated_from_an_input_with_an_invalid_item()
         self::bindInput($input);
 
         $this->expectException(InvalidArgumentException::class);
-        $this->expectExceptionMessage('Invalid item type. Expected a string, got "object".');
+        $this->expectExceptionMessage('Invalid item type. Expected a string, got "stdClass".');
 
         ParallelizationInput::fromInput($input);
     }
@@ -196,8 +196,8 @@ public static function inputProvider(): iterable
         yield 'item passed' => [
             new StringInput('item15'),
             new ParallelizationInput(
-                false,
-                $findNumberOfProcesses,
+                true,
+                1,
                 'item15',
                 false,
             ),
@@ -206,8 +206,8 @@ public static function inputProvider(): iterable
         yield 'integer item passed' => [
             new ArrayInput(['item' => 10]),
             new ParallelizationInput(
-                false,
-                $findNumberOfProcesses,
+                true,
+                1,
                 '10',
                 false,
             ),
@@ -216,8 +216,8 @@ public static function inputProvider(): iterable
         yield 'float item passed' => [
             new ArrayInput(['item' => -.5]),
             new ParallelizationInput(
-                false,
-                $findNumberOfProcesses,
+                true,
+                1,
                 '-0.5',
                 false,
             ),
diff --git a/tests/Integration/ParallelizationIntegrationTest.php b/tests/Integration/ParallelizationIntegrationTest.php
index 122ba87..9e02262 100644
--- a/tests/Integration/ParallelizationIntegrationTest.php
+++ b/tests/Integration/ParallelizationIntegrationTest.php
@@ -102,6 +102,36 @@ public function test_it_can_run_the_command_without_sub_processes(): void
         self::assertSame($expected, $actual, $actual);
     }
 
+    public function test_it_processes_the_item_in_the_main_process_if_an_item_is_passed(): void
+    {
+        $commandTester = $this->noSubProcessCommandTester;
+
+        $commandTester->execute(
+            [
+                'command' => 'test:no-subprocess',
+                'item' => 'item0',
+            ],
+            ['interactive' => true],
+        );
+
+        // TODO: note that the "in 1 process is incorrect here..."
+        $expected = <<<'EOF'
+            Processing 1 item, batches of 2, 1 batch
+
+             0/1 [>---------------------------]   0% 10 secs/10 secs 10.0 MiB
+             1/1 [============================] 100% 10 secs/10 secs 10.0 MiB
+
+            Processed 1 item.
+
+            EOF;
+
+        $actual = self::normalizeIntermediateFixedProgressBars(
+            $this->getOutput($commandTester),
+        );
+
+        self::assertSame($expected, $actual, $actual);
+    }
+
     public function test_it_uses_a_sub_process_if_only_one_process_is_used(): void
     {
         $commandTester = $this->noSubProcessCommandTester;