diff --git a/NEWS b/NEWS
index af80e9a4bb6..1f7febd25da 100644
--- a/NEWS
+++ b/NEWS
@@ -51,6 +51,10 @@ PHP                                                                        NEWS
   . Partially fixed bug GH-17387 (Trivial crash in phpdbg lexer). (nielsdos)
   . Fix memory leak in phpdbg calling registered function. (nielsdos)
 
+- Reflection:
+  . Fixed bug GH-15902 (Core dumped in ext/reflection/php_reflection.c).
+    (DanielEScherzer)
+
 - Streams:
   . Fixed bug GH-17650 (realloc with size 0 in user_filters.c). (nielsdos)
   . Fix memory leak on overflow in _php_stream_scandir(). (nielsdos)
diff --git a/ext/reflection/php_reflection.c b/ext/reflection/php_reflection.c
index 8cecc108339..50dcd489c87 100644
--- a/ext/reflection/php_reflection.c
+++ b/ext/reflection/php_reflection.c
@@ -649,13 +649,20 @@ static int format_default_value(smart_str *str, zval *value) {
 		} ZEND_HASH_FOREACH_END();
 		smart_str_appendc(str, ']');
 	} else if (Z_TYPE_P(value) == IS_OBJECT) {
-		/* This branch may only be reached for default properties, which don't support arbitrary objects. */
+		/* This branch is reached if the constant AST was already evaluated and
+		 * resulted in an object; show enum names, or the type of non-enums
+		 * (GH-15902) */
 		zend_object *obj = Z_OBJ_P(value);
 		zend_class_entry *class = obj->ce;
-		ZEND_ASSERT(class->ce_flags & ZEND_ACC_ENUM);
-		smart_str_append(str, class->name);
-		smart_str_appends(str, "::");
-		smart_str_append(str, Z_STR_P(zend_enum_fetch_case_name(obj)));
+		if (class->ce_flags & ZEND_ACC_ENUM) {
+			smart_str_append(str, class->name);
+			smart_str_appends(str, "::");
+			smart_str_append(str, Z_STR_P(zend_enum_fetch_case_name(obj)));
+		} else {
+			smart_str_appends(str, "object(");
+			smart_str_append(str, class->name);
+			smart_str_appends(str, ")");
+		}
 	} else {
 		ZEND_ASSERT(Z_TYPE_P(value) == IS_CONSTANT_AST);
 		zend_string *ast_str = zend_ast_export("", Z_ASTVAL_P(value), "");
diff --git a/ext/reflection/tests/gh15902/ReflectionClass-callable.phpt b/ext/reflection/tests/gh15902/ReflectionClass-callable.phpt
new file mode 100644
index 00000000000..0ed02dd837c
--- /dev/null
+++ b/ext/reflection/tests/gh15902/ReflectionClass-callable.phpt
@@ -0,0 +1,37 @@
+--TEST--
+ReflectionClass object default property - used to say "callable"
+--INI--
+opcache.enable_cli=0
+--FILE--
+<?php
+
+class C {
+	public stdClass $a = FOO;
+}
+define('FOO', new stdClass);
+
+new C;
+
+$reflector = new ReflectionClass(C::class);
+echo $reflector;
+?>
+--EXPECTF--
+Class [ <user> class C ] {
+  @@ %sReflectionClass-callable.php %d-%d
+
+  - Constants [0] {
+  }
+
+  - Static properties [0] {
+  }
+
+  - Static methods [0] {
+  }
+
+  - Properties [1] {
+    Property [ public stdClass $a = object(stdClass) ]
+  }
+
+  - Methods [0] {
+  }
+}
diff --git a/ext/reflection/tests/gh15902/ReflectionClass-class.phpt b/ext/reflection/tests/gh15902/ReflectionClass-class.phpt
new file mode 100644
index 00000000000..cb03cdd383f
--- /dev/null
+++ b/ext/reflection/tests/gh15902/ReflectionClass-class.phpt
@@ -0,0 +1,38 @@
+--TEST--
+ReflectionClass object default property - used to say "__CLASS__"
+--INI--
+opcache.enable_cli=0
+--FILE--
+<?php
+
+class C {
+	public stdClass $a = FOO;
+}
+$reflector = new ReflectionClass(C::class);
+
+define('FOO', new stdClass);
+new C;
+
+echo $reflector;
+
+?>
+--EXPECTF--
+Class [ <user> class C ] {
+  @@ %sReflectionClass-class.php %d-%d
+
+  - Constants [0] {
+  }
+
+  - Static properties [0] {
+  }
+
+  - Static methods [0] {
+  }
+
+  - Properties [1] {
+    Property [ public stdClass $a = object(stdClass) ]
+  }
+
+  - Methods [0] {
+  }
+}
diff --git a/ext/reflection/tests/gh15902/ReflectionProperty-callable.phpt b/ext/reflection/tests/gh15902/ReflectionProperty-callable.phpt
new file mode 100644
index 00000000000..b88d52721fc
--- /dev/null
+++ b/ext/reflection/tests/gh15902/ReflectionProperty-callable.phpt
@@ -0,0 +1,20 @@
+--TEST--
+ReflectionProperty object default - used to say "callable"
+--INI--
+opcache.enable_cli=0
+--FILE--
+<?php
+
+class C {
+	public stdClass $a = FOO;
+}
+define('FOO', new stdClass);
+
+new C;
+
+$reflector = new ReflectionProperty(C::class, 'a');
+echo $reflector;
+
+?>
+--EXPECTF--
+Property [ public stdClass $a = object(stdClass) ]
diff --git a/ext/reflection/tests/gh15902/ReflectionProperty-class.phpt b/ext/reflection/tests/gh15902/ReflectionProperty-class.phpt
new file mode 100644
index 00000000000..021df4fe87b
--- /dev/null
+++ b/ext/reflection/tests/gh15902/ReflectionProperty-class.phpt
@@ -0,0 +1,20 @@
+--TEST--
+ReflectionProperty object default - used to say "__CLASS__"
+--INI--
+opcache.enable_cli=0
+--FILE--
+<?php
+
+class C {
+	public stdClass $a = FOO;
+}
+$reflector = new ReflectionProperty(C::class, 'a');
+
+define('FOO', new stdClass);
+new C;
+
+echo $reflector;
+
+?>
+--EXPECTF--
+Property [ public stdClass $a = object(stdClass) ]