diff --git a/schemars/src/_private.rs b/schemars/src/_private.rs
index 657244b..5b03178 100644
--- a/schemars/src/_private.rs
+++ b/schemars/src/_private.rs
@@ -161,7 +161,7 @@ pub mod metadata {
     add_metadata_fn!(add_deprecated, deprecated, bool);
     add_metadata_fn!(add_read_only, read_only, bool);
     add_metadata_fn!(add_write_only, write_only, bool);
-    add_metadata_fn!(add_default, default, Value);
+    add_metadata_fn!(add_default, default, Option<Value>);
 
     pub fn add_examples<I: IntoIterator<Item = Value>>(schema: Schema, examples: I) -> Schema {
         let mut schema_obj = schema.into_object();
diff --git a/schemars/tests/default.rs b/schemars/tests/default.rs
index fbc1033..ab489f5 100644
--- a/schemars/tests/default.rs
+++ b/schemars/tests/default.rs
@@ -30,6 +30,7 @@ where
 struct MyStruct {
     my_int: i32,
     my_bool: bool,
+    my_optional_string: Option<String>,
     #[serde(serialize_with = "custom_serialize")]
     my_struct2: MyStruct2,
     #[serde(
diff --git a/schemars/tests/expected/default.json b/schemars/tests/expected/default.json
index aefef83..4155d53 100644
--- a/schemars/tests/expected/default.json
+++ b/schemars/tests/expected/default.json
@@ -12,6 +12,13 @@
       "default": false,
       "type": "boolean"
     },
+    "my_optional_string": {
+      "default": null,
+      "type": [
+        "string",
+        "null"
+      ]
+    },
     "my_struct2": {
       "default": "i:0 b:false",
       "allOf": [