diff --git a/src/Reflection/InitializerExprTypeResolver.php b/src/Reflection/InitializerExprTypeResolver.php
index f7a8f872e2..5e5336da67 100644
--- a/src/Reflection/InitializerExprTypeResolver.php
+++ b/src/Reflection/InitializerExprTypeResolver.php
@@ -2611,6 +2611,22 @@ public function getUnaryMinusType(Expr $expr, callable $getTypeCallback): Type
 	{
 		$type = $getTypeCallback($expr);
 
+		// GMP supports unary minus and returns GMP
+		$gmpType = new ObjectType('GMP');
+		if ($gmpType->isSuperTypeOf($type)->yes()) {
+			return $gmpType;
+		}
+
+		// Handle union types containing GMP
+		if ($gmpType->isSuperTypeOf($type)->maybe()) {
+			$nonGmpType = TypeCombinator::remove($type, $gmpType);
+			$nonGmpResult = $this->getUnaryMinusTypeFromType($expr, $nonGmpType);
+			if ($nonGmpResult instanceof IntegerRangeType) {
+				$nonGmpResult = $getTypeCallback(new Expr\BinaryOp\Mul($expr, new Int_(-1)));
+			}
+			return TypeCombinator::union($gmpType, $nonGmpResult);
+		}
+
 		$type = $this->getUnaryMinusTypeFromType($expr, $type);
 		if ($type instanceof IntegerRangeType) {
 			return $getTypeCallback(new Expr\BinaryOp\Mul($expr, new Int_(-1)));
@@ -2652,6 +2668,19 @@ public function getBitwiseNotType(Expr $expr, callable $getTypeCallback): Type
 	{
 		$exprType = $getTypeCallback($expr);
 
+		// GMP supports bitwise not and returns GMP
+		$gmpType = new ObjectType('GMP');
+		if ($gmpType->isSuperTypeOf($exprType)->yes()) {
+			return $gmpType;
+		}
+
+		// Handle union types containing GMP
+		if ($gmpType->isSuperTypeOf($exprType)->maybe()) {
+			$nonGmpType = TypeCombinator::remove($exprType, $gmpType);
+			$nonGmpResult = $this->getBitwiseNotTypeFromType($nonGmpType);
+			return TypeCombinator::union($gmpType, $nonGmpResult);
+		}
+
 		return $this->getBitwiseNotTypeFromType($exprType);
 	}
 
diff --git a/src/Type/Php/GmpOperatorTypeSpecifyingExtension.php b/src/Type/Php/GmpOperatorTypeSpecifyingExtension.php
new file mode 100644
index 0000000000..9e78d1c68e
--- /dev/null
+++ b/src/Type/Php/GmpOperatorTypeSpecifyingExtension.php
@@ -0,0 +1,74 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Type\Php;
+
+use PHPStan\DependencyInjection\AutowiredService;
+use PHPStan\Type\BooleanType;
+use PHPStan\Type\IntegerRangeType;
+use PHPStan\Type\NeverType;
+use PHPStan\Type\ObjectType;
+use PHPStan\Type\OperatorTypeSpecifyingExtension;
+use PHPStan\Type\Type;
+use function in_array;
+
+#[AutowiredService]
+final class GmpOperatorTypeSpecifyingExtension implements OperatorTypeSpecifyingExtension
+{
+
+	public function isOperatorSupported(string $operatorSigil, Type $leftSide, Type $rightSide): bool
+	{
+		if ($leftSide instanceof NeverType || $rightSide instanceof NeverType) {
+			return false;
+		}
+
+		if (!in_array($operatorSigil, ['+', '-', '*', '/', '**', '%', '&', '|', '^', '<<', '>>', '<', '<=', '>', '>=', '==', '!=', '<=>'], true)) {
+			return false;
+		}
+
+		$gmpType = new ObjectType('GMP');
+		$leftIsGmp = $gmpType->isSuperTypeOf($leftSide)->yes();
+		$rightIsGmp = $gmpType->isSuperTypeOf($rightSide)->yes();
+
+		// At least one side must be GMP
+		if (!$leftIsGmp && !$rightIsGmp) {
+			return false;
+		}
+
+		// The other side must be GMP-compatible (GMP, int, or numeric-string)
+		// GMP operations with incompatible types (like stdClass) will error at runtime
+		return $this->isGmpCompatible($leftSide, $gmpType) && $this->isGmpCompatible($rightSide, $gmpType);
+	}
+
+	private function isGmpCompatible(Type $type, ObjectType $gmpType): bool
+	{
+		if ($gmpType->isSuperTypeOf($type)->yes()) {
+			return true;
+		}
+		if ($type->isInteger()->yes()) {
+			return true;
+		}
+		if ($type->isNumericString()->yes()) {
+			return true;
+		}
+		return false;
+	}
+
+	public function specifyType(string $operatorSigil, Type $leftSide, Type $rightSide): Type
+	{
+		$gmpType = new ObjectType('GMP');
+
+		// Comparison operators return bool or int (for spaceship)
+		if (in_array($operatorSigil, ['<', '<=', '>', '>=', '==', '!='], true)) {
+			return new BooleanType();
+		}
+
+		if ($operatorSigil === '<=>') {
+			return IntegerRangeType::fromInterval(-1, 1);
+		}
+
+		// All arithmetic and bitwise operations on GMP return GMP
+		// GMP can operate with: GMP, int, or numeric-string
+		return $gmpType;
+	}
+
+}
diff --git a/tests/PHPStan/Analyser/nsrt/gmp-operators.php b/tests/PHPStan/Analyser/nsrt/gmp-operators.php
new file mode 100644
index 0000000000..d99a9a500a
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/gmp-operators.php
@@ -0,0 +1,215 @@
+<?php
+
+namespace GmpOperatorsTest;
+
+use function PHPStan\Testing\assertType;
+
+// =============================================================================
+// Operator overloads
+// =============================================================================
+
+function gmpArithmeticOperators(\GMP $a, \GMP $b): void
+{
+	assertType('GMP', $a + $b);
+	assertType('GMP', $a - $b);
+	assertType('GMP', $a * $b);
+	assertType('GMP', $a / $b);
+	assertType('GMP', $a % $b);
+	assertType('GMP', $a ** $b);
+	assertType('GMP', -$a);
+}
+
+function gmpWithIntOperators(\GMP $a, int $i): void
+{
+	// GMP on left
+	assertType('GMP', $a + $i);
+	assertType('GMP', $a - $i);
+	assertType('GMP', $a * $i);
+	assertType('GMP', $a / $i);
+	assertType('GMP', $a % $i);
+	assertType('GMP', $a ** $i);
+
+	// int on left (GMP on right)
+	assertType('GMP', $i + $a);
+	assertType('GMP', $i - $a);
+	assertType('GMP', $i * $a);
+	assertType('GMP', $i / $a);
+	assertType('GMP', $i % $a);
+	// Note: $i ** $a is not supported by GMP - exponent must be int
+}
+
+function gmpBitwiseOperators(\GMP $a, \GMP $b, int $i): void
+{
+	// GMP bitwise with GMP
+	assertType('GMP', $a & $b);
+	assertType('GMP', $a | $b);
+	assertType('GMP', $a ^ $b);
+	assertType('GMP', ~$a);
+	assertType('GMP', $a << $b);
+	assertType('GMP', $a >> $b);
+
+	// GMP on left, int on right
+	assertType('GMP', $a & $i);
+	assertType('GMP', $a | $i);
+	assertType('GMP', $a ^ $i);
+	assertType('GMP', $a << $i);
+	assertType('GMP', $a >> $i);
+
+	// int on left, GMP on right
+	assertType('GMP', $i & $a);
+	assertType('GMP', $i | $a);
+	assertType('GMP', $i ^ $a);
+}
+
+function gmpComparisonOperators(\GMP $a, \GMP $b, int $i): void
+{
+	// GMP compared with GMP
+	assertType('bool', $a < $b);
+	assertType('bool', $a <= $b);
+	assertType('bool', $a > $b);
+	assertType('bool', $a >= $b);
+	assertType('bool', $a == $b);
+	assertType('bool', $a != $b);
+	assertType('int<-1, 1>', $a <=> $b);
+
+	// GMP on left, int on right
+	assertType('bool', $a < $i);
+	assertType('bool', $a <= $i);
+	assertType('bool', $a > $i);
+	assertType('bool', $a >= $i);
+	assertType('bool', $a == $i);
+	assertType('bool', $a != $i);
+	assertType('int<-1, 1>', $a <=> $i);
+
+	// int on left, GMP on right
+	assertType('bool', $i < $a);
+	assertType('bool', $i <= $a);
+	assertType('bool', $i > $a);
+	assertType('bool', $i >= $a);
+	assertType('bool', $i == $a);
+	assertType('bool', $i != $a);
+	assertType('int<-1, 1>', $i <=> $a);
+}
+
+function gmpAssignmentOperators(\GMP $a, int $i): void
+{
+	$x = $a;
+	$x += $i;
+	assertType('GMP', $x);
+
+	$y = $a;
+	$y -= $i;
+	assertType('GMP', $y);
+
+	$z = $a;
+	$z *= $i;
+	assertType('GMP', $z);
+}
+
+// =============================================================================
+// gmp_* functions (corresponding to operator overloads)
+// =============================================================================
+
+function gmpArithmeticFunctions(\GMP $a, \GMP $b, int $i): void
+{
+	// gmp_add corresponds to +
+	assertType('GMP', gmp_add($a, $b));
+	assertType('GMP', gmp_add($a, $i));
+	assertType('GMP', gmp_add($i, $a));
+
+	// gmp_sub corresponds to -
+	assertType('GMP', gmp_sub($a, $b));
+	assertType('GMP', gmp_sub($a, $i));
+	assertType('GMP', gmp_sub($i, $a));
+
+	// gmp_mul corresponds to *
+	assertType('GMP', gmp_mul($a, $b));
+	assertType('GMP', gmp_mul($a, $i));
+	assertType('GMP', gmp_mul($i, $a));
+
+	// gmp_div_q corresponds to /
+	assertType('GMP', gmp_div_q($a, $b));
+	assertType('GMP', gmp_div_q($a, $i));
+
+	// gmp_div is alias of gmp_div_q
+	assertType('GMP', gmp_div($a, $b));
+
+	// gmp_mod corresponds to %
+	assertType('GMP', gmp_mod($a, $b));
+	assertType('GMP', gmp_mod($a, $i));
+
+	// gmp_pow corresponds to **
+	assertType('GMP', gmp_pow($a, 2));
+	assertType('GMP', gmp_pow($a, $i));
+
+	// gmp_neg corresponds to unary -
+	assertType('GMP', gmp_neg($a));
+
+	// gmp_abs (no direct operator)
+	assertType('GMP', gmp_abs($a));
+}
+
+function gmpBitwiseFunctions(\GMP $a, \GMP $b): void
+{
+	// gmp_and corresponds to &
+	assertType('GMP', gmp_and($a, $b));
+
+	// gmp_or corresponds to |
+	assertType('GMP', gmp_or($a, $b));
+
+	// gmp_xor corresponds to ^
+	assertType('GMP', gmp_xor($a, $b));
+
+	// gmp_com corresponds to ~
+	assertType('GMP', gmp_com($a));
+}
+
+function gmpComparisonFunctions(\GMP $a, \GMP $b, int $i): void
+{
+	// gmp_cmp returns -1, 0, or 1 in practice, but stubs say int
+	// TODO: Could be improved to int<-1, 1> like the <=> operator
+	assertType('int', gmp_cmp($a, $b));
+	assertType('int', gmp_cmp($a, $i));
+}
+
+function gmpFromInit(): void
+{
+	$x = gmp_init('1');
+	assertType('GMP', $x);
+
+	// Operator with gmp_init result
+	$y = $x * 2;
+	assertType('GMP', $y);
+
+	$z = $x + gmp_init('5');
+	assertType('GMP', $z);
+}
+
+function gmpWithNumericString(\GMP $a, string $s): void
+{
+	// GMP functions accept numeric strings
+	assertType('GMP', gmp_add($a, '123'));
+	assertType('GMP', gmp_mul($a, '456'));
+}
+
+// =============================================================================
+// Union types - unary operators handle GMP in unions correctly
+// =============================================================================
+
+/**
+ * @param \GMP|int $maybeGmp
+ */
+function gmpUnionUnaryMinus($maybeGmp): void
+{
+	// Unary minus on GMP|int returns GMP (from GMP branch) | int (from int branch)
+	assertType('GMP|int', -$maybeGmp);
+}
+
+/**
+ * @param \GMP|int $maybeGmp
+ */
+function gmpUnionBitwiseNot($maybeGmp): void
+{
+	// Bitwise NOT on GMP|int returns GMP (from GMP branch) | int (from int branch)
+	assertType('GMP|int', ~$maybeGmp);
+}