diff --git a/phpunit/code/constant-overflow-warning.php b/phpunit/code/constant-overflow-warning.php
new file mode 100644
index 00000000..e0800681
--- /dev/null
+++ b/phpunit/code/constant-overflow-warning.php
@@ -0,0 +1,10 @@
+<?php
+
+declare(strict_types=1);
+
+function main(): void
+{
+    $a = PHP_INT_MAX + 1;
+    $b = PHP_INT_MAX * 2;
+    $c = 1 + 2;
+}
diff --git a/phpunit/code/shift-boundary-native-neg-left.php b/phpunit/code/shift-boundary-native-neg-left.php
new file mode 100644
index 00000000..7750dd8e
--- /dev/null
+++ b/phpunit/code/shift-boundary-native-neg-left.php
@@ -0,0 +1,9 @@
+<?php
+
+declare(strict_types=1);
+use native_types;
+
+function main(): void
+{
+    var_dump(-1 << 2);
+}
diff --git a/phpunit/code/shift-boundary-native-neg-right.php b/phpunit/code/shift-boundary-native-neg-right.php
new file mode 100644
index 00000000..4bc22055
--- /dev/null
+++ b/phpunit/code/shift-boundary-native-neg-right.php
@@ -0,0 +1,9 @@
+<?php
+
+declare(strict_types=1);
+use native_types;
+
+function main(): void
+{
+    var_dump(-8 >> 2);
+}
diff --git a/phpunit/code/shift-boundary-native-negative.php b/phpunit/code/shift-boundary-native-negative.php
new file mode 100644
index 00000000..e6de2d2b
--- /dev/null
+++ b/phpunit/code/shift-boundary-native-negative.php
@@ -0,0 +1,9 @@
+<?php
+
+declare(strict_types=1);
+use native_types;
+
+function main(): void
+{
+    var_dump(1 >> -1);
+}
diff --git a/phpunit/code/shift-boundary-native-ok.php b/phpunit/code/shift-boundary-native-ok.php
new file mode 100644
index 00000000..2547a6ca
--- /dev/null
+++ b/phpunit/code/shift-boundary-native-ok.php
@@ -0,0 +1,11 @@
+<?php
+
+declare(strict_types=1);
+use native_types;
+
+function main(): void
+{
+    var_dump(1 << 3);
+    var_dump(5 >> 1);
+    var_dump(8 >> 2);
+}
diff --git a/phpunit/code/shift-boundary-native-overflow.php b/phpunit/code/shift-boundary-native-overflow.php
new file mode 100644
index 00000000..08ea1c60
--- /dev/null
+++ b/phpunit/code/shift-boundary-native-overflow.php
@@ -0,0 +1,9 @@
+<?php
+
+declare(strict_types=1);
+use native_types;
+
+function main(): void
+{
+    var_dump(1 << 64);
+}
diff --git a/phpunit/code/shift-boundary-native-sign-bit.php b/phpunit/code/shift-boundary-native-sign-bit.php
new file mode 100644
index 00000000..0ac507ec
--- /dev/null
+++ b/phpunit/code/shift-boundary-native-sign-bit.php
@@ -0,0 +1,9 @@
+<?php
+
+declare(strict_types=1);
+use native_types;
+
+function main(): void
+{
+    var_dump(1 << 63);
+}
diff --git a/phpunit/code/shift-boundary-warning.php b/phpunit/code/shift-boundary-warning.php
new file mode 100644
index 00000000..794c75f0
--- /dev/null
+++ b/phpunit/code/shift-boundary-warning.php
@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+function main(): void
+{
+    $a = 1 << 64;
+    $b = 1 >> 64;
+    $c = -1 >> 64;
+    $d = 1 >> -1;
+    $e = 1 << 2;
+    $f = 3 >> 1;
+}
diff --git a/phpunit/src/ConstantArithmeticOverflowTest.php b/phpunit/src/ConstantArithmeticOverflowTest.php
new file mode 100644
index 00000000..917a98b5
--- /dev/null
+++ b/phpunit/src/ConstantArithmeticOverflowTest.php
@@ -0,0 +1,70 @@
+<?php
+
+namespace TypePhp\Tests;
+
+use PHPUnit\Framework\TestCase;
+use PhpParser\Node;
+use TypePhp\CompilerTest;
+use TypePhp\Diagnostics\DiagnosticReporter;
+use TypePhp\Exception\TestError;
+
+/**
+ * Constant integer arithmetic overflow emits compile-time warnings and folds
+ * to the PHP float result in non-native mode.
+ */
+class ConstantArithmeticOverflowTest extends TestCase
+{
+    public function testOverflowingConstantArithmeticEmitsWarning(): void
+    {
+        $reporter = $this->compileWithReporter();
+
+        $overflowWarnings = array_values(array_filter(
+            $reporter->warnings,
+            fn (string $message): bool => str_contains($message, 'Constant integer arithmetic overflows int64')
+        ));
+        $this->assertCount(2, $overflowWarnings);
+        $this->assertStringContainsString('9223372036854775807 + 1', $overflowWarnings[0]);
+        $this->assertStringContainsString('folding to PHP float result', $overflowWarnings[0]);
+    }
+
+    public function testNonOverflowingConstantArithmeticDoesNotWarn(): void
+    {
+        $reporter = $this->compileWithReporter();
+
+        foreach ($reporter->warnings as $message) {
+            $this->assertStringNotContainsString('1 + 2', $message);
+        }
+    }
+
+    /**
+     * @return object{warnings: list<string>}
+     */
+    private function compileWithReporter(): object
+    {
+        global $translator;
+        $compiler = CompilerTest::create(ROOT_PATH);
+        $translator = $compiler;
+        $reporter = new class implements DiagnosticReporter {
+            /** @var list<string> */
+            public array $warnings = [];
+
+            public function fatal(string $message): never
+            {
+                throw new TestError($message);
+            }
+
+            public function warning(Node $node, string $file, string $message): void
+            {
+                $this->warnings[] = $message;
+            }
+        };
+        $compiler->setDiagnosticReporter($reporter);
+
+        $testFile = __DIR__ . '/../code/constant-overflow-warning.php';
+        $compiler->addFiles([$testFile]);
+        $compiler->prepareFile($testFile);
+        $compiler->convertFile($testFile);
+
+        return $reporter;
+    }
+}
diff --git a/phpunit/src/ShiftBoundaryTest.php b/phpunit/src/ShiftBoundaryTest.php
new file mode 100644
index 00000000..3f7ea29e
--- /dev/null
+++ b/phpunit/src/ShiftBoundaryTest.php
@@ -0,0 +1,149 @@
+<?php
+
+namespace TypePhp\Tests;
+
+use PHPUnit\Framework\TestCase;
+use PhpParser\Node;
+use TypePhp\CompilerTest;
+use TypePhp\Diagnostics\DiagnosticReporter;
+use TypePhp\Exception\TestError;
+
+/**
+ * Constant bit shift boundaries emit compile-time warnings and keep PHP
+ * semantics in non-native mode.
+ */
+class ShiftBoundaryTest extends TestCase
+{
+    public function testShiftCountAtLeastWordSizeEmitsWarning(): void
+    {
+        $reporter = $this->compileWithReporter();
+
+        $overflowWarnings = array_values(array_filter(
+            $reporter->warnings,
+            fn (string $message): bool => str_contains($message, 'Bit shift count 64 is >= 64')
+        ));
+        $this->assertCount(3, $overflowWarnings);
+        foreach ($overflowWarnings as $message) {
+            $this->assertStringContainsString('folding with PHP semantics', $message);
+        }
+    }
+
+    public function testNegativeShiftCountEmitsWarning(): void
+    {
+        $reporter = $this->compileWithReporter();
+
+        $negativeWarnings = array_values(array_filter(
+            $reporter->warnings,
+            fn (string $message): bool => str_contains($message, 'Bit shift by a negative number')
+        ));
+        $this->assertCount(1, $negativeWarnings);
+        $this->assertStringContainsString('ArithmeticError', $negativeWarnings[0]);
+    }
+
+    public function testInRangeShiftDoesNotWarn(): void
+    {
+        $reporter = $this->compileWithReporter();
+
+        foreach ($reporter->warnings as $message) {
+            $this->assertStringNotContainsString('Bit shift count 2 is >=', $message);
+            $this->assertStringNotContainsString('Bit shift count 1 is >=', $message);
+        }
+    }
+
+    public function testNativeModeRejectsShiftCountAtLeastWordSize(): void
+    {
+        $this->expectException(TestError::class);
+        $this->expectExceptionMessage('Bit shift count 64 is >= 64 and is not supported in native mode');
+        $this->compileNativeWithReporter('shift-boundary-native-overflow.php');
+    }
+
+    public function testNativeModeRejectsNegativeShiftCount(): void
+    {
+        $this->expectException(TestError::class);
+        $this->expectExceptionMessage('Bit shift by a negative number is not supported in native mode');
+        $this->compileNativeWithReporter('shift-boundary-native-negative.php');
+    }
+
+    public function testNativeModeRejectsNegativeRightShift(): void
+    {
+        $this->expectException(TestError::class);
+        $this->expectExceptionMessage('Right shift of a negative value is implementation-defined in C++');
+        $this->compileNativeWithReporter('shift-boundary-native-neg-right.php');
+    }
+
+    public function testNativeModeRejectsLeftShiftChangingSignBit(): void
+    {
+        $this->expectException(TestError::class);
+        $this->expectExceptionMessage('Left shift that changes the sign bit is undefined behavior in C++');
+        $this->compileNativeWithReporter('shift-boundary-native-sign-bit.php');
+    }
+
+    public function testNativeModeRejectsNegativeLeftShift(): void
+    {
+        $this->expectException(TestError::class);
+        $this->expectExceptionMessage('Left shift of a negative value is undefined behavior in C++');
+        $this->compileNativeWithReporter('shift-boundary-native-neg-left.php');
+    }
+
+    public function testNativeModeAllowsInRangeShift(): void
+    {
+        $compiler = $this->compileNativeWithReporter('shift-boundary-native-ok.php');
+        $this->assertNotNull($compiler);
+    }
+
+    /**
+     * @return object{warnings: list<string>}
+     */
+    private function compileWithReporter(): object
+    {
+        global $translator;
+        $compiler = CompilerTest::create(ROOT_PATH);
+        $translator = $compiler;
+        $reporter = new class implements DiagnosticReporter {
+            /** @var list<string> */
+            public array $warnings = [];
+
+            public function fatal(string $message): never
+            {
+                throw new TestError($message);
+            }
+
+            public function warning(Node $node, string $file, string $message): void
+            {
+                $this->warnings[] = $message;
+            }
+        };
+        $compiler->setDiagnosticReporter($reporter);
+
+        $testFile = __DIR__ . '/../code/shift-boundary-warning.php';
+        $compiler->addFiles([$testFile]);
+        $compiler->prepareFile($testFile);
+        $compiler->convertFile($testFile);
+
+        return $reporter;
+    }
+
+    private function compileNativeWithReporter(string $file): CompilerTest
+    {
+        global $translator;
+        $compiler = CompilerTest::create(ROOT_PATH);
+        $translator = $compiler;
+        $compiler->setDiagnosticReporter(new class implements DiagnosticReporter {
+            public function fatal(string $message): never
+            {
+                throw new TestError($message);
+            }
+
+            public function warning(Node $node, string $file, string $message): void
+            {
+            }
+        });
+
+        $testFile = __DIR__ . '/../code/' . $file;
+        $compiler->addFiles([$testFile]);
+        $compiler->prepareFile($testFile);
+        $compiler->convertFile($testFile);
+
+        return $compiler;
+    }
+}
diff --git a/src/Parser/BinaryOpTrait.php b/src/Parser/BinaryOpTrait.php
index e40cb3ef..9f3719e7 100644
--- a/src/Parser/BinaryOpTrait.php
+++ b/src/Parser/BinaryOpTrait.php
@@ -132,6 +132,13 @@ trait BinaryOpTrait
             return 'php::fn::mod(' . $leftExpr . ', ' . $rightExpr . ')';
         }
 
+        if ($op === '<<' || $op === '>>') {
+            $foldedShift = $this->tryFoldConstantShift($left, $right, $op, $leftExpr, $rightExpr);
+            if ($foldedShift !== null) {
+                return $foldedShift;
+            }
+        }
+
         $folded = $this->tryFoldConstantIntArithmetic($left, $right, $op);
         if ($folded !== null) {
             return $folded;
@@ -140,6 +147,104 @@ trait BinaryOpTrait
         return '((' . $leftExpr . ') ' . $op . ' (' . $rightExpr . '))';
     }
 
+    /**
+     * Fold constant integer shifts to PHP semantics in non-native mode.
+     *
+     * PHP shifts by >= word size to 0 (left) or -1/0 (right, arithmetic), and
+     * throws a catchable ArithmeticError for negative shift counts. Native C++
+     * shifts are undefined for those counts, so the constant case is folded
+     * (>= word size) or routed through php::Var (negative, so the Zend shift
+     * function raises the catchable error at runtime).
+     */
+    protected function tryFoldConstantShift(
+        NodeAbstract $left,
+        NodeAbstract $right,
+        string $op,
+        string $leftExpr,
+        string $rightExpr
+    ): ?string {
+        $leftValue = $this->constantIntValue($left);
+        $shiftValue = $this->constantIntValue($right);
+        if ($leftValue === null || $shiftValue === null) {
+            return null;
+        }
+
+        $wordSize = PHP_INT_SIZE * 8;
+
+        if ($this->nativeTypes) {
+            if ($shiftValue >= $wordSize) {
+                $this->fatalError(
+                    $right,
+                    'Bit shift count ' . $shiftValue . ' is >= ' . $wordSize
+                        . ' and is not supported in native mode'
+                );
+            }
+            if ($shiftValue < 0) {
+                $this->fatalError(
+                    $right,
+                    'Bit shift by a negative number is not supported in native mode'
+                );
+            }
+            if ($op === '>>' && $leftValue < 0) {
+                $this->fatalError(
+                    $left,
+                    'Right shift of a negative value is implementation-defined in C++'
+                        . ' and is not supported in native mode'
+                );
+            }
+            if ($op === '<<' && $leftValue < 0) {
+                $this->fatalError(
+                    $left,
+                    'Left shift of a negative value is undefined behavior in C++'
+                        . ' and is not supported in native mode'
+                );
+            }
+            if ($op === '<<' && $this->leftShiftTouchesSignBit($leftValue, $shiftValue)) {
+                $this->fatalError(
+                    $left,
+                    'Left shift that changes the sign bit is undefined behavior in C++'
+                        . ' and is not supported in native mode'
+                );
+            }
+            return null;
+        }
+
+        if ($shiftValue >= $wordSize) {
+            $result = $op === '<<' ? '0LL' : ($leftValue < 0 ? '-1LL' : '0LL');
+            $this->warning(
+                $right,
+                'Bit shift count ' . $shiftValue . ' is >= ' . $wordSize
+                    . '; folding with PHP semantics (left shift to 0, right shift to -1 for negative operands, 0 otherwise)'
+            );
+            return $result;
+        }
+
+        if ($shiftValue < 0) {
+            $this->warning(
+                $right,
+                'Bit shift by a negative number throws ArithmeticError at runtime'
+            );
+            // Route through php::Var so the Zend shift function raises the catchable error.
+            return '((php::Var(' . $leftExpr . ')) ' . $op . ' (php::Var(' . $rightExpr . ')))';
+        }
+
+        return null;
+    }
+
+    /**
+     * Whether a constant left shift of a non-negative value would set the sign
+     * bit (overflow the signed range), which is undefined behavior in C++.
+     */
+    protected function leftShiftTouchesSignBit(int $value, int $shift): bool
+    {
+        if ($value < 0 || $shift <= 0) {
+            return false;
+        }
+        // PHP shift is performed on unsigned values; a negative result means
+        // the sign bit got set.
+        return ($value << $shift) < 0;
+    }
+
     /**
      * Fold constant int arithmetic that would overflow int64 in generated C++.
      *
@@ -181,6 +286,11 @@ trait BinaryOpTrait
             return null;
         }
 
+        $this->warning(
+            $left,
+            'Constant integer arithmetic overflows int64; folding to PHP float result ('
+                . $leftValue . ' ' . $op . ' ' . $rightValue . ')'
+        );
         return $this->genFloatLiteral($result);
     }
 
diff --git a/tests/compiler/constant-shift-boundaries.phpt b/tests/compiler/constant-shift-boundaries.phpt
new file mode 100644
index 00000000..3ea27138
--- /dev/null
+++ b/tests/compiler/constant-shift-boundaries.phpt
@@ -0,0 +1,33 @@
+--TEST--
+Constant bit shift boundaries follow PHP semantics
+--FILE--
+<?php
+declare(strict_types=1);
+
+function main(): void
+{
+    var_dump(1 << 64);
+    var_dump(1 >> 64);
+    var_dump(-1 >> 64);
+    var_dump(PHP_INT_MIN >> 64);
+    var_dump(1 >> 63);
+    var_dump(-1 >> 63);
+    var_dump(1 << 63);
+    var_dump(5 >> 1);
+    try {
+        var_dump(1 >> -1);
+    } catch (ArithmeticError $e) {
+        echo "caught: " . $e->getMessage() . "\n";
+    }
+}
+?>
+--EXPECTF--
+int(0)
+int(0)
+int(-1)
+int(-1)
+int(0)
+int(-1)
+int(-9223372036854775808)
+int(2)
+caught: Bit shift by negative number