diff --git a/ext/standard/JitNumberFormat.php b/ext/standard/JitNumberFormat.php
index d153fded28b..30c2315e15b 100644
--- a/ext/standard/JitNumberFormat.php
+++ b/ext/standard/JitNumberFormat.php
@@ -8,8 +8,8 @@
 use PHPCompiler\JIT\BasicBlockHelper;
 use PHPCompiler\JIT\Builtin\TypeErrorRaise;
 use PHPCompiler\JIT\Context;
-use PHPCompiler\JIT\JitStringBuiltinArg;
 use PHPCompiler\JIT\JitRoundModeArg;
+use PHPCompiler\JIT\JitStringBuiltinArg;
 use PHPCompiler\JIT\JitValueBox;
 use PHPCompiler\JIT\NamedOptionalCallArgs;
 use PHPCompiler\JIT\Variable as JITVariable;
@@ -18,9 +18,9 @@
 use PHPLLVM\Value;
 
 /**
- * LLVM JIT/AOT helper for number_format() (int/float/numeric string, 0–4 args; subset of PHP).
+ * LLVM JIT/AOT helper for number_format() (int/float/numeric string, 0–5 args; subset of PHP).
  *
- * php-src: ext/standard/number_format.c — Z_PARAM_LONG / Z_PARAM_STR
+ * php-src: ext/standard/number_format.c — Z_PARAM_LONG / Z_PARAM_STR / RoundingMode
  */
 final class JitNumberFormat
 {
@@ -29,9 +29,10 @@ public static function format(Context $context, JITVariable ...$args): Value
         $argc = count($args);
         $maxArgs = CompilerVersion::supportsRoundingModeEnum() ? 5 : 4;
         if ($argc < 1 || $argc > $maxArgs) {
-            throw new \LogicException(
-                sprintf('number_format() requires one to %d arguments', $maxArgs)
-            );
+            throw new \LogicException(\sprintf(
+                'number_format() requires one to %d arguments',
+                $maxArgs
+            ));
         }
 
         if ($context->callerStrictTypes) {
diff --git a/ext/standard/VmNumberFormat.php b/ext/standard/VmNumberFormat.php
index ddb9730a4c9..ee828f8ec40 100644
--- a/ext/standard/VmNumberFormat.php
+++ b/ext/standard/VmNumberFormat.php
@@ -81,11 +81,7 @@ public static function format(
             $pow *= 10;
         }
 
-        if ($decimals > 0) {
-            $rounded = VmRound::mathRound($number, $decimals, $roundingMode);
-        } else {
-            $rounded = VmRound::mathRound($number, 0, $roundingMode);
-        }
+        $rounded = VmRound::mathRound($number, $decimals, $roundingMode);
 
         $intPart = (int) floor($rounded);
         $fracPart = 0;
diff --git a/ext/standard/number_format.php b/ext/standard/number_format.php
index 2eb4a520375..2128da6cdea 100644
--- a/ext/standard/number_format.php
+++ b/ext/standard/number_format.php
@@ -23,7 +23,7 @@
 /**
  * number_format() for integers and floats (C-style locale subset; LLVM JIT/AOT).
  *
- * php-src: ext/standard/number_format.c — Z_PARAM_LONG / Z_PARAM_STR
+ * php-src: ext/standard/number_format.c — Z_PARAM_LONG / Z_PARAM_STR / RoundingMode
  */
 final class number_format extends Internal
 {
@@ -74,7 +74,7 @@ public function execute(Frame $frame): void
                 'number_format',
                 3,
                 'thousands_separator'
-            )             ?? ','
+            ) ?? ','
             : ',';
         $roundingMode = StdlibConstants::PHP_ROUND_HALF_UP;
         if (CompilerVersion::supportsRoundingModeEnum() && isset($frame->calledArgs[4])) {
diff --git a/test/compliance/cases/stdlib/number_format_rounding_mode.phpt b/test/compliance/cases/stdlib/number_format_rounding_mode.phpt
index 47883ec7710..1452da1ce6f 100644
--- a/test/compliance/cases/stdlib/number_format_rounding_mode.phpt
+++ b/test/compliance/cases/stdlib/number_format_rounding_mode.phpt
@@ -1,15 +1,24 @@
 --TEST--
-number_format() optional RoundingMode (PHP 8.4, #9438)
---EXTENSIONS--
+stdlib number_format() optional rounding_mode (PHP 8.4, ext/standard/number_format.c, #9438)
 --FILE--
 <?php
-if (!enum_exists('RoundingMode')) {
+declare(strict_types=1);
+
+if (!enum_exists('RoundingMode', false)) {
     echo "skip\n";
     exit(0);
 }
-echo number_format(1.55, 1, '.', '', RoundingMode::HalfAwayFromZero), "\n";
-echo number_format(2.5, 0, '.', '', RoundingMode::HalfEven), "\n";
-?>
+
+var_export(number_format(2.5, 0, '.', '', RoundingMode::HalfAwayFromZero));
+echo "\n";
+var_export(number_format(2.5, 0, '.', '', RoundingMode::TowardsZero));
+echo "\n";
+var_export(number_format(1.55, 1, '.', '', RoundingMode::HalfAwayFromZero));
+echo "\n";
+var_export(number_format(2.5, 0, '.', '', RoundingMode::HalfEven));
+echo "\n";
 --EXPECT--
-1.6
-2
+'3'
+'2'
+'1.6'
+'2'
diff --git a/test/compliance/cases/stdlib/number_format_rounding_mode_jit.phpt b/test/compliance/cases/stdlib/number_format_rounding_mode_jit.phpt
new file mode 100644
index 00000000000..0fcd11b3466
--- /dev/null
+++ b/test/compliance/cases/stdlib/number_format_rounding_mode_jit.phpt
@@ -0,0 +1,11 @@
+--TEST--
+stdlib number_format() optional rounding_mode JIT (#9438, ext/standard/number_format.c)
+--FILE--
+<?php
+declare(strict_types=1);
+
+echo number_format(2.5, 0, '.', '', RoundingMode::HalfAwayFromZero), "\n";
+echo number_format(2.5, 0, '.', '', RoundingMode::TowardsZero), "\n";
+--EXPECT--
+3
+2
diff --git a/test/fixtures/aot/cases/number_format_rounding_mode.phpt b/test/fixtures/aot/cases/number_format_rounding_mode.phpt
new file mode 100644
index 00000000000..8d375f9954d
--- /dev/null
+++ b/test/fixtures/aot/cases/number_format_rounding_mode.phpt
@@ -0,0 +1,11 @@
+--TEST--
+AOT: number_format() optional rounding_mode (#9438, ext/standard/number_format.c)
+--FILE--
+<?php
+declare(strict_types=1);
+
+echo number_format(2.5, 0, '.', '', RoundingMode::HalfAwayFromZero), "\n";
+echo number_format(2.5, 0, '.', '', RoundingMode::TowardsZero), "\n";
+--EXPECT--
+3
+2
diff --git a/test/repro/maintainer_gap_number_format_rounding_mode.php b/test/repro/maintainer_gap_number_format_rounding_mode.php
index 0605eccdfe5..d802e2454e9 100644
--- a/test/repro/maintainer_gap_number_format_rounding_mode.php
+++ b/test/repro/maintainer_gap_number_format_rounding_mode.php
@@ -2,20 +2,32 @@
 
 declare(strict_types=1);
 
-if (!enum_exists('RoundingMode')) {
-    fwrite(STDERR, "skip: RoundingMode not on reference profile\n");
+if (!enum_exists('RoundingMode', false)) {
+    echo "skip: RoundingMode not on reference profile\n";
     exit(0);
 }
 
-$got = number_format(1.55, 1, '.', '', RoundingMode::HalfAwayFromZero);
-if ('1.6' !== $got) {
-    echo 'fail: got ', var_export($got, true), "\n";
+$halfUp = number_format(2.5, 0, '.', '', RoundingMode::HalfAwayFromZero);
+if ('3' !== $halfUp) {
+    echo 'fail: HalfAwayFromZero got ', var_export($halfUp, true), " expected '3'\n";
     exit(1);
 }
 
-$gotEven = number_format(2.5, 0, '.', '', RoundingMode::HalfEven);
-if ('2' !== $gotEven) {
-    echo 'fail even: got ', var_export($gotEven, true), "\n";
+$towardsZero = number_format(2.5, 0, '.', '', RoundingMode::TowardsZero);
+if ('2' !== $towardsZero) {
+    echo 'fail: TowardsZero got ', var_export($towardsZero, true), " expected '2'\n";
+    exit(1);
+}
+
+$oneDecimal = number_format(1.55, 1, '.', '', RoundingMode::HalfAwayFromZero);
+if ('1.6' !== $oneDecimal) {
+    echo 'fail: 1.55/1 decimal got ', var_export($oneDecimal, true), " expected '1.6'\n";
+    exit(1);
+}
+
+$halfEven = number_format(2.5, 0, '.', '', RoundingMode::HalfEven);
+if ('2' !== $halfEven) {
+    echo 'fail even: got ', var_export($halfEven, true), " expected '2'\n";
     exit(1);
 }
 
diff --git a/test/unit/StringFormatRuntimeShrinkTest.php b/test/unit/StringFormatRuntimeShrinkTest.php
index ad60414e1e1..0fae13ffe45 100644
--- a/test/unit/StringFormatRuntimeShrinkTest.php
+++ b/test/unit/StringFormatRuntimeShrinkTest.php
@@ -5,6 +5,7 @@
 namespace PHPCompiler\Test\Unit;
 
 use PHPCompiler\ext\standard\SprintfJitHelper;
+use PHPCompiler\ext\standard\StdlibConstants;
 use PHPCompiler\ext\standard\VmNumberFormat;
 use PHPCompiler\ext\standard\VmSprintf;
 use PHPUnit\Framework\TestCase;
@@ -47,5 +48,19 @@ public function testSprintfJitHelperNumberFormatMatchesVmNumberFormat(): void
             SprintfJitHelper::numberFormat(1234.5, 2, '.', ',')
         );
         $this->assertSame('nan', SprintfJitHelper::numberFormat(NAN, 0, '.', ','));
+        $this->assertSame(
+            '3',
+            SprintfJitHelper::numberFormat(2.5, 0, '.', '', StdlibConstants::PHP_ROUND_HALF_UP)
+        );
+        $this->assertSame(
+            '2',
+            SprintfJitHelper::numberFormat(
+                2.5,
+                0,
+                '.',
+                '',
+                StdlibConstants::PHP_ROUND_TOWARD_ZERO
+            )
+        );
     }
 }