diff --git a/core/Cargo.toml b/core/Cargo.toml
index a456d3bf2..3a607f085 100644
--- a/core/Cargo.toml
+++ b/core/Cargo.toml
@@ -38,7 +38,6 @@ actix-web-validator3 = { version = "3.0", optional = true, package = "actix-web-
 validator12 = { version = "0.12", features = ["derive"], optional = true, package = "validator" }
 validator14 = { version = "0.14", features = ["derive"], optional = true, package = "validator" }
 openapiv3 = { version = "1.0.3", optional = true }
-indexmap = { version = "2.0", features = ["serde"], optional = true }
 
 [features]
 # actix-web support
@@ -54,7 +53,7 @@ nightly = ["paperclip-macros/nightly"]
 
 # OpenAPI support (v2 and codegen)
 v2 = ["paperclip-macros/v2"]
-v3 = ["v2", "openapiv3", "indexmap"]
+v3 = ["v2", "openapiv3"]
 codegen = ["v2", "heck", "log"]
 uuid = ["uuid0"]
 uuid0 = ["uuid0_dep"]
diff --git a/core/src/lib.rs b/core/src/lib.rs
index ea7851d0f..80a317bcd 100644
--- a/core/src/lib.rs
+++ b/core/src/lib.rs
@@ -15,7 +15,7 @@ pub mod im;
 pub mod util;
 #[cfg(feature = "v2")]
 pub mod v2;
-#[cfg(feature = "v3")]
+// #[cfg(feature = "v3")]
 pub mod v3;
 
 pub use self::error::ValidationError;
diff --git a/core/src/v2/models.rs b/core/src/v2/models.rs
index a686c0e1e..66055fb7d 100644
--- a/core/src/v2/models.rs
+++ b/core/src/v2/models.rs
@@ -84,6 +84,7 @@ pub enum DataTypeFormat {
     Other,
 }
 
+#[allow(clippy::to_string_trait_impl)]
 impl ToString for DataTypeFormat {
     fn to_string(&self) -> String {
         match self {
@@ -439,7 +440,7 @@ pub struct PathItem<P, R> {
 impl<S> PathItem<Parameter<S>, Response<S>> {
     /// Normalizes this operation map.
     /// - Collects and removes parameters shared across operations
-    /// and adds them to the list global to this map.
+    ///   and adds them to the list global to this map.
     pub fn normalize(&mut self) {
         // We're using `Option<BTreeSet>` over `BTreeSet` because we need to
         // differentiate between the first operation that we use for initial
diff --git a/core/src/v2/schema.rs b/core/src/v2/schema.rs
index 0baa2ae76..2f945e7fb 100644
--- a/core/src/v2/schema.rs
+++ b/core/src/v2/schema.rs
@@ -257,11 +257,11 @@ impl_type_simple!(std::net::Ipv6Addr, DataType::String, DataTypeFormat::IpV6);
 /// framework-specific macros:
 ///
 /// - [`Apiv2Schema`](https://paperclip-rs.github.io/paperclip/paperclip_actix/derive.Apiv2Schema.html)
-/// for schema objects.
+///   for schema objects.
 /// - [`Apiv2Security`](https://paperclip-rs.github.io/paperclip/paperclip_actix/derive.Apiv2Security.html)
-/// for security scheme objects.
+///   for security scheme objects.
 /// - [`Apiv2Header`](https://paperclip-rs.github.io/paperclip/paperclip_actix/derive.Apiv2Header.html)
-/// for header parameters objects.
+///   for header parameters objects.
 ///
 /// This is implemented for primitive types by default.
 pub trait Apiv2Schema {
diff --git a/core/src/v3/contact.rs b/core/src/v3/contact.rs
index 603628cd5..911bbfd48 100644
--- a/core/src/v3/contact.rs
+++ b/core/src/v3/contact.rs
@@ -6,7 +6,7 @@ impl From<v2::Contact> for openapiv3::Contact {
             name: v2.name,
             url: v2.url,
             email: v2.email,
-            extensions: indexmap::IndexMap::new(),
+            extensions: Default::default(),
         }
     }
 }
diff --git a/core/src/v3/external_documentation.rs b/core/src/v3/external_documentation.rs
index 5e2262a31..1e6923a1d 100644
--- a/core/src/v3/external_documentation.rs
+++ b/core/src/v3/external_documentation.rs
@@ -5,7 +5,7 @@ impl From<v2::ExternalDocs> for openapiv3::ExternalDocumentation {
         openapiv3::ExternalDocumentation {
             description: v2.description,
             url: v2.url,
-            extensions: indexmap::IndexMap::new(),
+            extensions: Self::default().extensions,
         }
     }
 }
diff --git a/core/src/v3/header.rs b/core/src/v3/header.rs
index f3a21abcf..99ab77e94 100644
--- a/core/src/v3/header.rs
+++ b/core/src/v3/header.rs
@@ -7,10 +7,10 @@ impl From<v2::Header> for openapiv3::Header {
             style: Default::default(),
             required: false,
             deprecated: None,
-            format: openapiv3::ParameterSchemaOrContent::Content(indexmap::IndexMap::new()),
+            format: openapiv3::ParameterSchemaOrContent::Content(Default::default()),
             example: None,
-            extensions: indexmap::IndexMap::new(),
-            examples: indexmap::IndexMap::new(),
+            extensions: Default::default(),
+            examples: Default::default(),
         }
     }
 }
diff --git a/core/src/v3/info.rs b/core/src/v3/info.rs
index 790824e47..1afb64700 100644
--- a/core/src/v3/info.rs
+++ b/core/src/v3/info.rs
@@ -9,13 +9,13 @@ impl From<v2::Info> for openapiv3::Info {
             contact: v2.contact.map(|c| c.into()),
             license: v2.license.map(From::from),
             version: v2.version,
-            extensions: v2.extensions.into_iter().fold(
-                indexmap::IndexMap::new(),
-                |mut i, (k, v)| {
+            extensions: v2
+                .extensions
+                .into_iter()
+                .fold(Default::default(), |mut i, (k, v)| {
                     i.insert(k, v);
                     i
-                },
-            ),
+                }),
         }
     }
 }
diff --git a/core/src/v3/license.rs b/core/src/v3/license.rs
index 9b18e051c..c1937829d 100644
--- a/core/src/v3/license.rs
+++ b/core/src/v3/license.rs
@@ -5,7 +5,7 @@ impl From<v2::License> for openapiv3::License {
         openapiv3::License {
             name: v2.name.unwrap_or_default(),
             url: v2.url,
-            extensions: indexmap::IndexMap::new(),
+            extensions: Default::default(),
         }
     }
 }
diff --git a/core/src/v3/openapi.rs b/core/src/v3/openapi.rs
index 6f051e6ad..ce9e1fd6c 100644
--- a/core/src/v3/openapi.rs
+++ b/core/src/v3/openapi.rs
@@ -17,22 +17,19 @@ impl From<v2::DefaultApiRaw> for openapiv3::OpenAPI {
                 .security_schemes
                 .insert(name, openapiv3::ReferenceOr::Item(scheme.into()));
         }
-        components.responses = v2
-            .responses
-            .iter()
-            .fold(indexmap::IndexMap::new(), |mut i, b| {
-                i.insert(b.0.to_string(), b.1.clone().into());
+        components.responses = v2.responses.iter().fold(Default::default(), |mut i, b| {
+            i.insert(b.0.to_string(), b.1.clone().into());
+            i
+        });
+        spec.extensions = v2
+            .extensions
+            .into_iter()
+            .fold(Default::default(), |mut i, (k, v)| {
+                i.insert(k, v);
                 i
             });
-        spec.extensions =
-            v2.extensions
-                .into_iter()
-                .fold(indexmap::IndexMap::new(), |mut i, (k, v)| {
-                    i.insert(k, v);
-                    i
-                });
         spec.paths = openapiv3::Paths {
-            paths: v2.paths.iter().fold(indexmap::IndexMap::new(), |mut i, b| {
+            paths: v2.paths.iter().fold(Default::default(), |mut i, b| {
                 i.insert(
                     b.0.to_string(),
                     openapiv3::ReferenceOr::Item(b.1.clone().into()),
@@ -42,13 +39,10 @@ impl From<v2::DefaultApiRaw> for openapiv3::OpenAPI {
             ..Default::default()
         };
 
-        components.schemas = v2
-            .definitions
-            .iter()
-            .fold(indexmap::IndexMap::new(), |mut i, b| {
-                i.insert(b.0.to_string(), b.1.clone().into());
-                i
-            });
+        components.schemas = v2.definitions.iter().fold(Default::default(), |mut i, b| {
+            i.insert(b.0.to_string(), b.1.clone().into());
+            i
+        });
         spec.components = Some(components);
 
         spec
@@ -77,7 +71,7 @@ fn openapi3_servers(
                         url: format!("{}://{}{}", scheme_str, host, base.as_deref().unwrap_or("")),
                         description: None,
                         variables: None,
-                        extensions: indexmap::IndexMap::new(),
+                        extensions: Default::default(),
                     }
                 })
                 .collect()
@@ -86,7 +80,7 @@ fn openapi3_servers(
                 url: format!("//{}{}", host, base.as_deref().unwrap_or("")),
                 description: None,
                 variables: None,
-                extensions: indexmap::IndexMap::new(),
+                extensions: Default::default(),
             }]
         }
     } else {
@@ -94,7 +88,7 @@ fn openapi3_servers(
             url: base.unwrap_or_else(|| "/".to_string()),
             description: None,
             variables: None,
-            extensions: indexmap::IndexMap::new(),
+            extensions: Default::default(),
         }]
     }
 }
diff --git a/core/src/v3/operation.rs b/core/src/v3/operation.rs
index a7498634a..3f7c1bc38 100644
--- a/core/src/v3/operation.rs
+++ b/core/src/v3/operation.rs
@@ -85,10 +85,9 @@ impl From<v2::Operation<v2::DefaultParameterRaw, v2::DefaultResponseRaw>> for op
             request_body,
             responses: openapiv3::Responses {
                 default: None,
-                responses: v2
-                    .responses
-                    .iter()
-                    .fold(indexmap::IndexMap::new(), |mut i, (k, v)| {
+                responses: v2.responses.iter().fold(
+                    openapiv3::Responses::default().responses,
+                    |mut i, (k, v)| {
                         if let Ok(code) = k.parse::<u16>() {
                             let code = openapiv3::StatusCode::Code(code);
                             i.insert(
@@ -101,7 +100,8 @@ impl From<v2::Operation<v2::DefaultParameterRaw, v2::DefaultResponseRaw>> for op
                             );
                         }
                         i
-                    }),
+                    },
+                ),
                 ..Default::default()
             },
             deprecated: v2.deprecated,
@@ -112,16 +112,19 @@ impl From<v2::Operation<v2::DefaultParameterRaw, v2::DefaultResponseRaw>> for op
                     v2.security
                         .iter()
                         .map(|s| {
-                            s.iter().fold(indexmap::IndexMap::new(), |mut i, (k, v)| {
-                                i.insert(k.to_string(), v.clone());
-                                i
-                            })
+                            s.iter().fold(
+                                openapiv3::SecurityRequirement::default(),
+                                |mut i, (k, v)| {
+                                    i.insert(k.to_string(), v.clone());
+                                    i
+                                },
+                            )
                         })
                         .collect(),
                 )
             },
             servers: vec![],
-            extensions: indexmap::IndexMap::new(),
+            extensions: Default::default(),
         }
     }
 }
diff --git a/core/src/v3/paths.rs b/core/src/v3/paths.rs
index 5e516b67f..a78073b53 100644
--- a/core/src/v3/paths.rs
+++ b/core/src/v3/paths.rs
@@ -26,7 +26,7 @@ impl From<v2::DefaultPathItemRaw> for openapiv3::PathItem {
                 })
                 .parameters
             },
-            extensions: indexmap::IndexMap::new(),
+            extensions: Default::default(),
             description: None,
             summary: None,
         }
diff --git a/core/src/v3/request_body.rs b/core/src/v3/request_body.rs
index 378155b18..6e355deba 100644
--- a/core/src/v3/request_body.rs
+++ b/core/src/v3/request_body.rs
@@ -19,9 +19,9 @@ impl From<v2::DefaultParameterRaw>
                 ))),
             },
             example: None,
-            examples: indexmap::IndexMap::new(),
+            examples: Default::default(),
             explode: None,
-            extensions: indexmap::IndexMap::new(),
+            extensions: Default::default(),
         };
 
         match v2.in_ {
@@ -49,12 +49,12 @@ impl From<v2::DefaultParameterRaw>
                         schema: v2.schema.map(|s| s.into()),
                         ..Default::default()
                     };
-                    let mut map = indexmap::IndexMap::new();
+                    let mut map = openapiv3::RequestBody::default().content;
                     map.insert(v2::SpecFormat::Json.mime().0.to_string(), media);
                     map
                 },
                 required: v2.required,
-                extensions: indexmap::IndexMap::new(),
+                extensions: Default::default(),
             })),
         }
     }
diff --git a/core/src/v3/response.rs b/core/src/v3/response.rs
index f626bcac7..1ac0a8dba 100644
--- a/core/src/v3/response.rs
+++ b/core/src/v3/response.rs
@@ -13,7 +13,7 @@ impl From<OperationResponse<'_>> for openapiv3::Response {
                 .response
                 .headers
                 .iter()
-                .fold(indexmap::IndexMap::new(), |mut i, b| {
+                .fold(Default::default(), |mut i, b| {
                     i.insert(
                         b.0.to_string(),
                         openapiv3::ReferenceOr::Item(b.1.clone().into()),
@@ -34,7 +34,7 @@ impl From<OperationResponse<'_>> for openapiv3::Response {
                             ..Default::default()
                         };
 
-                        let mut map = indexmap::IndexMap::new();
+                        let mut map = openapiv3::Response::default().content;
                         match v2.operation.produces.as_ref() {
                             Some(range) => {
                                 for mime in range {
@@ -52,11 +52,11 @@ impl From<OperationResponse<'_>> for openapiv3::Response {
                         }
                         map
                     }
-                    None => indexmap::IndexMap::new(),
+                    None => Default::default(),
                 }
             },
-            extensions: indexmap::IndexMap::new(),
-            links: indexmap::IndexMap::new(),
+            extensions: Default::default(),
+            links: Default::default(),
         }
     }
 }
@@ -72,13 +72,13 @@ impl From<OperationEitherResponse<'_>> for openapiv3::ReferenceOr<openapiv3::Res
             Either::Left(reference) => {
                 let response = openapiv3::Response {
                     description: "".to_string(),
-                    headers: indexmap::IndexMap::new(),
+                    headers: Default::default(),
                     content: {
                         let media = openapiv3::MediaType {
                             schema: Some(reference.into()),
                             ..Default::default()
                         };
-                        let mut map = indexmap::IndexMap::new();
+                        let mut map = openapiv3::Response::default().content;
                         match v2.operation.produces.as_ref() {
                             Some(range) => {
                                 for mime in range {
@@ -92,8 +92,8 @@ impl From<OperationEitherResponse<'_>> for openapiv3::ReferenceOr<openapiv3::Res
                         }
                         map
                     },
-                    links: indexmap::IndexMap::new(),
-                    extensions: indexmap::IndexMap::new(),
+                    links: Default::default(),
+                    extensions: Default::default(),
                 };
                 openapiv3::ReferenceOr::Item(response)
             }
diff --git a/core/src/v3/schema.rs b/core/src/v3/schema.rs
index 149dc35fe..f174e6b55 100644
--- a/core/src/v3/schema.rs
+++ b/core/src/v3/schema.rs
@@ -30,7 +30,7 @@ impl From<v2::DefaultSchemaRaw> for openapiv3::ReferenceOr<openapiv3::Schema> {
                         description: v2.description,
                         discriminator: None,
                         default: None,
-                        extensions: indexmap::IndexMap::new(),
+                        extensions: Default::default(),
                     },
                     schema_kind: {
                         if let Some(data_type) = v2.data_type {
@@ -175,12 +175,10 @@ fn v2_data_type_to_v3(
         v2::DataType::Object => {
             openapiv3::SchemaKind::Type(openapiv3::Type::Object(openapiv3::ObjectType {
                 properties: {
-                    properties
-                        .iter()
-                        .fold(indexmap::IndexMap::new(), |mut i, b| {
-                            i.insert(b.0.to_string(), b.1.deref().clone().into());
-                            i
-                        })
+                    properties.iter().fold(Default::default(), |mut i, b| {
+                        i.insert(b.0.to_string(), b.1.deref().clone().into());
+                        i
+                    })
                 },
                 required: required.iter().cloned().collect::<Vec<_>>(),
                 additional_properties: None,
diff --git a/core/src/v3/security_scheme.rs b/core/src/v3/security_scheme.rs
index 5a0aa21ad..7f074da90 100644
--- a/core/src/v3/security_scheme.rs
+++ b/core/src/v3/security_scheme.rs
@@ -1,5 +1,14 @@
 use super::v2;
 
+macro_rules! to_indexmap {
+    ($v2:expr) => {
+        $v2.scopes.iter().fold(Default::default(), |mut i, (k, v)| {
+            i.insert(k.to_string(), v.to_string());
+            i
+        })
+    };
+}
+
 impl From<v2::SecurityScheme> for openapiv3::SecurityScheme {
     fn from(v2: v2::SecurityScheme) -> Self {
         match v2.type_.as_str() {
@@ -18,13 +27,6 @@ impl From<v2::SecurityScheme> for openapiv3::SecurityScheme {
                 description: v2.description,
             },
             "oauth2" => {
-                let scopes = v2
-                    .scopes
-                    .iter()
-                    .fold(indexmap::IndexMap::new(), |mut i, (k, v)| {
-                        i.insert(k.clone(), v.clone());
-                        i
-                    });
                 let flow = v2.flow.unwrap_or_default();
                 openapiv3::SecurityScheme::OAuth2 {
                     flows: openapiv3::OAuth2Flows {
@@ -32,7 +34,7 @@ impl From<v2::SecurityScheme> for openapiv3::SecurityScheme {
                             "implicit" => Some(openapiv3::OAuth2Flow::Implicit {
                                 authorization_url: v2.auth_url.clone().unwrap_or_default(),
                                 refresh_url: None,
-                                scopes: scopes.clone(),
+                                scopes: to_indexmap!(v2),
                             }),
                             _ => None,
                         },
@@ -40,7 +42,7 @@ impl From<v2::SecurityScheme> for openapiv3::SecurityScheme {
                             "password" => Some(openapiv3::OAuth2Flow::Password {
                                 refresh_url: None,
                                 token_url: v2.token_url.clone().unwrap_or_default(),
-                                scopes: scopes.clone(),
+                                scopes: to_indexmap!(v2),
                             }),
                             _ => None,
                         },
@@ -48,7 +50,7 @@ impl From<v2::SecurityScheme> for openapiv3::SecurityScheme {
                             "application" => Some(openapiv3::OAuth2Flow::ClientCredentials {
                                 refresh_url: None,
                                 token_url: v2.token_url.clone().unwrap_or_default(),
-                                scopes: scopes.clone(),
+                                scopes: to_indexmap!(v2),
                             }),
                             _ => None,
                         },
@@ -57,7 +59,7 @@ impl From<v2::SecurityScheme> for openapiv3::SecurityScheme {
                                 authorization_url: v2.auth_url.clone().unwrap_or_default(),
                                 token_url: v2.token_url.clone().unwrap_or_default(),
                                 refresh_url: None,
-                                scopes,
+                                scopes: to_indexmap!(v2),
                             }),
                             _ => None,
                         },
diff --git a/core/src/v3/tag.rs b/core/src/v3/tag.rs
index f55d1e44e..810548084 100644
--- a/core/src/v3/tag.rs
+++ b/core/src/v3/tag.rs
@@ -6,7 +6,7 @@ impl From<v2::Tag> for openapiv3::Tag {
             name: v2.name,
             description: v2.description,
             external_docs: v2.external_docs.map(openapiv3::ExternalDocumentation::from),
-            extensions: indexmap::IndexMap::new(),
+            extensions: Default::default(),
         }
     }
 }
diff --git a/src/error.rs b/src/error.rs
index 950aae9a3..f1a7c335c 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -59,10 +59,6 @@ pub enum PaperClipError {
     /// YAML coding errors.
     #[error("YAML error: {}", _0)]
     Yaml(serde_yaml::Error),
-    #[cfg(feature = "codegen-fmt")]
-    /// Errors from rustfmt.
-    #[error("Rustfmt formatting error: {}", _0)]
-    RustFmt(rustfmt_nightly::ErrorKind),
     #[cfg(feature = "codegen")]
     /// Errors in templating.
     #[error("Templating error: {}", _0)]
@@ -73,7 +69,5 @@ impl_err_from!(PaperClipError::std::io::Error > Io);
 impl_err_from!(PaperClipError::serde_json::Error > Json);
 impl_err_from!(PaperClipError::serde_yaml::Error > Yaml);
 impl_err_from!(PaperClipError::paperclip_core::ValidationError > Validation);
-#[cfg(feature = "codegen-fmt")]
-impl_err_from!(PaperClipError::rustfmt_nightly::ErrorKind > RustFmt);
 #[cfg(feature = "codegen")]
 impl_err_from!(PaperClipError::tinytemplate::error::Error > Templating);
diff --git a/src/v2/codegen/impls.rs b/src/v2/codegen/impls.rs
index a5f3c556e..4ce40cd34 100644
--- a/src/v2/codegen/impls.rs
+++ b/src/v2/codegen/impls.rs
@@ -926,7 +926,7 @@ impl<'a, 'b> SendableCodegen<'a, 'b> {
     /// Handle field for a form data parameter.
     fn handle_form_param(&mut self, field: StructField) {
         let name = object::to_snake_case(field.name);
-        if let Some(CollectionFormat::Multi) = field.delimiting.get(0) {
+        if let Some(CollectionFormat::Multi) = field.delimiting.first() {
             let _ = write!(
                 self.form,
                 "
@@ -988,7 +988,7 @@ impl<'a, 'b> SendableCodegen<'a, 'b> {
     /// Handle field for an URL query parameter.
     fn handle_query_param(&mut self, field: StructField) {
         let name = object::to_snake_case(field.name);
-        if let Some(CollectionFormat::Multi) = field.delimiting.get(0) {
+        if let Some(CollectionFormat::Multi) = field.delimiting.first() {
             self.multi_value_query.push(format!(
                 "
             &self.{}param_{}.as_ref().map(|v| {{
diff --git a/src/v2/codegen/object.rs b/src/v2/codegen/object.rs
index 3af6ae04e..3ddc7aa35 100644
--- a/src/v2/codegen/object.rs
+++ b/src/v2/codegen/object.rs
@@ -1005,7 +1005,7 @@ impl ApiObject {
 
         // FIXME: Currently, we're implementing the first value as enum default.
         // If "default" field exists, then we should use that instead.
-        if let Some(var) = self.variants().get(0) {
+        if let Some(var) = self.variants().first() {
             writeln!(
                 f,
                 "impl Default for {name} {{
diff --git a/src/v2/mod.rs b/src/v2/mod.rs
index 3105a30bb..22879f60a 100644
--- a/src/v2/mod.rs
+++ b/src/v2/mod.rs
@@ -60,9 +60,9 @@
 //! raw schema. During resolution, we:
 //!
 //! - walk through the nodes, find `$ref` fields and assign references to
-//! the actual definitions.
+//!   the actual definitions.
 //! - identify anonymous definitions in body parameters and response schemas
-//! and add them to the known map of definitions.
+//!   and add them to the known map of definitions.
 //!
 //! ```rust,no_run
 //! #[cfg(feature = "codegen")] {