diff --git a/NEWS b/NEWS
index 68577d27460..cfde633ce8d 100644
--- a/NEWS
+++ b/NEWS
@@ -2,6 +2,8 @@ PHP                                                                        NEWS
 |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 ?? ??? ????, PHP 8.4.0beta1
 
+- GMP:
+  . RFC: Change GMP bool cast behavior. (Saki Takamachi)
 
 01 Aug 2024, PHP 8.4.0alpha3
 
diff --git a/UPGRADING b/UPGRADING
index 1f4604cbfd6..a14711ed4ff 100644
--- a/UPGRADING
+++ b/UPGRADING
@@ -51,6 +51,9 @@ PHP 8.4 UPGRADE NOTES
 - GMP:
   . The GMP class is now final and cannot be extended anymore.
     RFC: https://wiki.php.net/rfc/gmp-final
+  . Casting a GMP object to bool changed so that 0 becomes false and everything else
+    becomes true.
+    RFC: https://wiki.php.net/rfc/fix_up_bcmath_number_class
 
 - Intl:
   . resourcebundle_get(), ResourceBundle::get(), and accessing offsets on a
diff --git a/ext/gmp/gmp.c b/ext/gmp/gmp.c
index 63838ad2a6e..09cbff82942 100644
--- a/ext/gmp/gmp.c
+++ b/ext/gmp/gmp.c
@@ -298,6 +298,10 @@ static zend_result gmp_cast_object(zend_object *readobj, zval *writeobj, int typ
 			ZVAL_DOUBLE(writeobj, mpz_get_d(gmpnum));
 		}
 		return SUCCESS;
+	case _IS_BOOL:
+		gmpnum = GET_GMP_OBJECT_FROM_OBJ(readobj)->num;
+		ZVAL_BOOL(writeobj, mpz_sgn(gmpnum) != 0);
+		return SUCCESS;
 	default:
 		return FAILURE;
 	}
diff --git a/ext/gmp/tests/cast.phpt b/ext/gmp/tests/cast.phpt
index 661a0159b94..864d8b2ad08 100644
--- a/ext/gmp/tests/cast.phpt
+++ b/ext/gmp/tests/cast.phpt
@@ -12,11 +12,25 @@ var_dump((int) $n);
 var_dump((float) $n);
 var_dump((bool) $n);
 
+echo "\n";
+
+$zero = gmp_init(0);
+echo $zero, "\n";
+var_dump((string) $zero);
+var_dump((int) $zero);
+var_dump((float) $zero);
+var_dump((bool) $zero);
+
 ?>
---EXPECTF--
+--EXPECT--
 42
 string(2) "42"
 int(42)
 float(42)
+bool(true)
 
-Recoverable fatal error: Object of class GMP could not be converted to bool in %s on line %d
+0
+string(1) "0"
+int(0)
+float(0)
+bool(false)