diff --git a/Cargo.toml b/Cargo.toml
index 41c11afa..b09c5f07 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -5,6 +5,7 @@ members = [
     "serde_derive_internals",
     "test_suite",
 ]
+resolver = "2"
 
 [patch.crates-io]
 serde = { path = "serde" }
diff --git a/serde/Cargo.toml b/serde/Cargo.toml
index 8c81e0f1..ae2855c5 100644
--- a/serde/Cargo.toml
+++ b/serde/Cargo.toml
@@ -6,7 +6,7 @@ build = "build.rs"
 categories = ["encoding", "no-std", "no-std::no-alloc"]
 description = "A generic serialization/deserialization framework"
 documentation = "https://docs.rs/serde"
-edition = "2018"
+edition = "2021"
 homepage = "https://serde.rs"
 keywords = ["serde", "serialization", "no_std"]
 license = "MIT OR Apache-2.0"
diff --git a/serde/src/de/mod.rs b/serde/src/de/mod.rs
index 540632f4..b2cc64c8 100644
--- a/serde/src/de/mod.rs
+++ b/serde/src/de/mod.rs
@@ -206,7 +206,7 @@ macro_rules! declare_error_trait {
             /// containing an integer, the unexpected type is the integer and the
             /// expected type is the string.
             #[cold]
-            fn invalid_type(unexp: Unexpected, exp: &Expected) -> Self {
+            fn invalid_type(unexp: Unexpected, exp: &dyn Expected) -> Self {
                 Error::custom(format_args!("invalid type: {}, expected {}", unexp, exp))
             }
 
@@ -224,7 +224,7 @@ macro_rules! declare_error_trait {
             /// that is not valid UTF-8, the unexpected value is the bytes and the
             /// expected value is a string.
             #[cold]
-            fn invalid_value(unexp: Unexpected, exp: &Expected) -> Self {
+            fn invalid_value(unexp: Unexpected, exp: &dyn Expected) -> Self {
                 Error::custom(format_args!("invalid value: {}, expected {}", unexp, exp))
             }
 
@@ -238,7 +238,7 @@ macro_rules! declare_error_trait {
             /// expected. For example `exp` might say that a tuple of size 6 was
             /// expected.
             #[cold]
-            fn invalid_length(len: usize, exp: &Expected) -> Self {
+            fn invalid_length(len: usize, exp: &dyn Expected) -> Self {
                 Error::custom(format_args!("invalid length {}, expected {}", len, exp))
             }
 
@@ -492,7 +492,7 @@ impl Expected for &str {
     }
 }
 
-impl Display for Expected + '_ {
+impl Display for dyn Expected + '_ {
     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
         Expected::fmt(self, formatter)
     }
diff --git a/serde/src/private/de.rs b/serde/src/private/de.rs
index 50ae6ed1..af5878bb 100644
--- a/serde/src/private/de.rs
+++ b/serde/src/private/de.rs
@@ -1065,7 +1065,7 @@ mod content {
         E: de::Error,
     {
         #[cold]
-        fn invalid_type(self, exp: &Expected) -> E {
+        fn invalid_type(self, exp: &dyn Expected) -> E {
             de::Error::invalid_type(self.content.unexpected(), exp)
         }
 
@@ -1654,7 +1654,7 @@ mod content {
         E: de::Error,
     {
         #[cold]
-        fn invalid_type(self, exp: &Expected) -> E {
+        fn invalid_type(self, exp: &dyn Expected) -> E {
             de::Error::invalid_type(self.content.unexpected(), exp)
         }
 
diff --git a/serde_derive/Cargo.toml b/serde_derive/Cargo.toml
index 4242312a..bce32311 100644
--- a/serde_derive/Cargo.toml
+++ b/serde_derive/Cargo.toml
@@ -5,7 +5,7 @@ authors = ["Erick Tryzelaar <erick.tryzelaar@gmail.com>", "David Tolnay <dtolnay
 categories = ["no-std", "no-std::no-alloc"]
 description = "Macros 1.1 implementation of #[derive(Serialize, Deserialize)]"
 documentation = "https://serde.rs/derive.html"
-edition = "2015"
+edition = "2021"
 exclude = ["build.rs"]
 homepage = "https://serde.rs"
 keywords = ["serde", "serialization", "no_std", "derive"]
diff --git a/serde_derive_internals/Cargo.toml b/serde_derive_internals/Cargo.toml
index 20bdbccc..4e494c83 100644
--- a/serde_derive_internals/Cargo.toml
+++ b/serde_derive_internals/Cargo.toml
@@ -4,7 +4,7 @@ version = "0.29.1"
 authors = ["Erick Tryzelaar <erick.tryzelaar@gmail.com>", "David Tolnay <dtolnay@gmail.com>"]
 description = "AST representation used by Serde derive macros. Unstable."
 documentation = "https://docs.rs/serde_derive_internals"
-edition = "2015"
+edition = "2021"
 exclude = ["build.rs"]
 homepage = "https://serde.rs"
 keywords = ["serde", "serialization"]