diff --git a/postgres/src/client.rs b/postgres/src/client.rs
index bbe4a8bc..90834508 100644
--- a/postgres/src/client.rs
+++ b/postgres/src/client.rs
@@ -1,6 +1,6 @@
 use crate::{
-    CancelToken, Config, CopyInWriter, CopyOutReader, GenericClient, RowIter, Statement,
-    ToStatement, Transaction, TransactionBuilder,
+    CancelToken, Config, CopyInWriter, CopyOutReader, RowIter, Statement, ToStatement, Transaction,
+    TransactionBuilder,
 };
 use std::ops::{Deref, DerefMut};
 use tokio::runtime::Runtime;
@@ -517,27 +517,3 @@ impl Client {
         self.client.is_closed()
     }
 }
-
-impl GenericClient for Client {
-    fn execute<T>(&mut self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<u64, Error>
-    where
-        T: ?Sized + ToStatement,
-    {
-        self.execute(query, params)
-    }
-
-    fn query<T>(&mut self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<Vec<Row>, Error>
-    where
-        T: ?Sized + ToStatement,
-    {
-        self.query(query, params)
-    }
-
-    fn prepare(&mut self, query: &str) -> Result<Statement, Error> {
-        self.prepare(query)
-    }
-
-    fn transaction(&mut self) -> Result<Transaction<'_>, Error> {
-        self.transaction()
-    }
-}
diff --git a/postgres/src/generic_client.rs b/postgres/src/generic_client.rs
index b586d0d4..42a466df 100644
--- a/postgres/src/generic_client.rs
+++ b/postgres/src/generic_client.rs
@@ -1,8 +1,17 @@
-use crate::types::ToSql;
-use crate::{Error, Row, Statement, ToStatement, Transaction};
+use crate::types::{ToSql, Type};
+use crate::{
+    Client, CopyInWriter, CopyOutReader, Error, Row, RowIter, SimpleQueryMessage, Statement,
+    ToStatement, Transaction,
+};
+
+mod private {
+    pub trait Sealed {}
+}
 
 /// A trait allowing abstraction over connections and transactions.
-pub trait GenericClient {
+///
+/// This trait is "sealed", and cannot be implemented outside of this crate.
+pub trait GenericClient: private::Sealed {
     /// Like `Client::execute`.
     fn execute<T>(&mut self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<u64, Error>
     where
@@ -13,9 +22,207 @@ pub trait GenericClient {
     where
         T: ?Sized + ToStatement;
 
+    /// Like `Client::query_one`.
+    fn query_one<T>(&mut self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<Row, Error>
+    where
+        T: ?Sized + ToStatement;
+
+    /// Like `Client::query_opt`.
+    fn query_opt<T>(
+        &mut self,
+        query: &T,
+        params: &[&(dyn ToSql + Sync)],
+    ) -> Result<Option<Row>, Error>
+    where
+        T: ?Sized + ToStatement;
+
+    /// Like `Client::query_raw`.
+    fn query_raw<'a, T, I>(&mut self, query: &T, params: I) -> Result<RowIter<'_>, Error>
+    where
+        T: ?Sized + ToStatement,
+        I: IntoIterator<Item = &'a dyn ToSql>,
+        I::IntoIter: ExactSizeIterator;
+
     /// Like `Client::prepare`.
     fn prepare(&mut self, query: &str) -> Result<Statement, Error>;
 
+    /// Like `Client::prepare_typed`.
+    fn prepare_typed(&mut self, query: &str, types: &[Type]) -> Result<Statement, Error>;
+
+    /// Like `Client::copy_in`.
+    fn copy_in<T>(&mut self, query: &T) -> Result<CopyInWriter<'_>, Error>
+    where
+        T: ?Sized + ToStatement;
+
+    /// Like `Client::copy_out`.
+    fn copy_out<T>(&mut self, query: &T) -> Result<CopyOutReader<'_>, Error>
+    where
+        T: ?Sized + ToStatement;
+
+    /// Like `Client::simple_query`.
+    fn simple_query(&mut self, query: &str) -> Result<Vec<SimpleQueryMessage>, Error>;
+
+    /// Like `Client::batch_execute`.
+    fn batch_execute(&mut self, query: &str) -> Result<(), Error>;
+
     /// Like `Client::transaction`.
     fn transaction(&mut self) -> Result<Transaction<'_>, Error>;
 }
+
+impl private::Sealed for Client {}
+
+impl GenericClient for Client {
+    fn execute<T>(&mut self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<u64, Error>
+    where
+        T: ?Sized + ToStatement,
+    {
+        self.execute(query, params)
+    }
+
+    fn query<T>(&mut self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<Vec<Row>, Error>
+    where
+        T: ?Sized + ToStatement,
+    {
+        self.query(query, params)
+    }
+
+    fn query_one<T>(&mut self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<Row, Error>
+    where
+        T: ?Sized + ToStatement,
+    {
+        self.query_one(query, params)
+    }
+
+    fn query_opt<T>(
+        &mut self,
+        query: &T,
+        params: &[&(dyn ToSql + Sync)],
+    ) -> Result<Option<Row>, Error>
+    where
+        T: ?Sized + ToStatement,
+    {
+        self.query_opt(query, params)
+    }
+
+    fn query_raw<'a, T, I>(&mut self, query: &T, params: I) -> Result<RowIter<'_>, Error>
+    where
+        T: ?Sized + ToStatement,
+        I: IntoIterator<Item = &'a dyn ToSql>,
+        I::IntoIter: ExactSizeIterator,
+    {
+        self.query_raw(query, params)
+    }
+
+    fn prepare(&mut self, query: &str) -> Result<Statement, Error> {
+        self.prepare(query)
+    }
+
+    fn prepare_typed(&mut self, query: &str, types: &[Type]) -> Result<Statement, Error> {
+        self.prepare_typed(query, types)
+    }
+
+    fn copy_in<T>(&mut self, query: &T) -> Result<CopyInWriter<'_>, Error>
+    where
+        T: ?Sized + ToStatement,
+    {
+        self.copy_in(query)
+    }
+
+    fn copy_out<T>(&mut self, query: &T) -> Result<CopyOutReader<'_>, Error>
+    where
+        T: ?Sized + ToStatement,
+    {
+        self.copy_out(query)
+    }
+
+    fn simple_query(&mut self, query: &str) -> Result<Vec<SimpleQueryMessage>, Error> {
+        self.simple_query(query)
+    }
+
+    fn batch_execute(&mut self, query: &str) -> Result<(), Error> {
+        self.batch_execute(query)
+    }
+
+    fn transaction(&mut self) -> Result<Transaction<'_>, Error> {
+        self.transaction()
+    }
+}
+
+impl private::Sealed for Transaction<'_> {}
+
+impl GenericClient for Transaction<'_> {
+    fn execute<T>(&mut self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<u64, Error>
+    where
+        T: ?Sized + ToStatement,
+    {
+        self.execute(query, params)
+    }
+
+    fn query<T>(&mut self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<Vec<Row>, Error>
+    where
+        T: ?Sized + ToStatement,
+    {
+        self.query(query, params)
+    }
+
+    fn query_one<T>(&mut self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<Row, Error>
+    where
+        T: ?Sized + ToStatement,
+    {
+        self.query_one(query, params)
+    }
+
+    fn query_opt<T>(
+        &mut self,
+        query: &T,
+        params: &[&(dyn ToSql + Sync)],
+    ) -> Result<Option<Row>, Error>
+    where
+        T: ?Sized + ToStatement,
+    {
+        self.query_opt(query, params)
+    }
+
+    fn query_raw<'a, T, I>(&mut self, query: &T, params: I) -> Result<RowIter<'_>, Error>
+    where
+        T: ?Sized + ToStatement,
+        I: IntoIterator<Item = &'a dyn ToSql>,
+        I::IntoIter: ExactSizeIterator,
+    {
+        self.query_raw(query, params)
+    }
+
+    fn prepare(&mut self, query: &str) -> Result<Statement, Error> {
+        self.prepare(query)
+    }
+
+    fn prepare_typed(&mut self, query: &str, types: &[Type]) -> Result<Statement, Error> {
+        self.prepare_typed(query, types)
+    }
+
+    fn copy_in<T>(&mut self, query: &T) -> Result<CopyInWriter<'_>, Error>
+    where
+        T: ?Sized + ToStatement,
+    {
+        self.copy_in(query)
+    }
+
+    fn copy_out<T>(&mut self, query: &T) -> Result<CopyOutReader<'_>, Error>
+    where
+        T: ?Sized + ToStatement,
+    {
+        self.copy_out(query)
+    }
+
+    fn simple_query(&mut self, query: &str) -> Result<Vec<SimpleQueryMessage>, Error> {
+        self.simple_query(query)
+    }
+
+    fn batch_execute(&mut self, query: &str) -> Result<(), Error> {
+        self.batch_execute(query)
+    }
+
+    fn transaction(&mut self) -> Result<Transaction<'_>, Error> {
+        self.transaction()
+    }
+}
diff --git a/postgres/src/transaction.rs b/postgres/src/transaction.rs
index c1fdcf06..e5b3682f 100644
--- a/postgres/src/transaction.rs
+++ b/postgres/src/transaction.rs
@@ -1,6 +1,5 @@
 use crate::{
-    CancelToken, CopyInWriter, CopyOutReader, GenericClient, Portal, RowIter, Rt, Statement,
-    ToStatement,
+    CancelToken, CopyInWriter, CopyOutReader, Portal, RowIter, Rt, Statement, ToStatement,
 };
 use tokio::runtime::Runtime;
 use tokio_postgres::types::{ToSql, Type};
@@ -185,27 +184,3 @@ impl<'a> Transaction<'a> {
         })
     }
 }
-
-impl<'a> GenericClient for Transaction<'a> {
-    fn execute<T>(&mut self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<u64, Error>
-    where
-        T: ?Sized + ToStatement,
-    {
-        self.execute(query, params)
-    }
-
-    fn query<T>(&mut self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<Vec<Row>, Error>
-    where
-        T: ?Sized + ToStatement,
-    {
-        self.query(query, params)
-    }
-
-    fn prepare(&mut self, query: &str) -> Result<Statement, Error> {
-        self.prepare(query)
-    }
-
-    fn transaction(&mut self) -> Result<Transaction<'_>, Error> {
-        self.transaction()
-    }
-}
diff --git a/tokio-postgres/src/client.rs b/tokio-postgres/src/client.rs
index 78f295e3..84ebfcbb 100644
--- a/tokio-postgres/src/client.rs
+++ b/tokio-postgres/src/client.rs
@@ -12,10 +12,8 @@ use crate::types::{Oid, ToSql, Type};
 use crate::Socket;
 use crate::{
     copy_in, copy_out, prepare, query, simple_query, slice_iter, CancelToken, CopyInSink, Error,
-    GenericClient, Row, SimpleQueryMessage, Statement, ToStatement, Transaction,
-    TransactionBuilder,
+    Row, SimpleQueryMessage, Statement, ToStatement, Transaction, TransactionBuilder,
 };
-use async_trait::async_trait;
 use bytes::{Buf, BytesMut};
 use fallible_iterator::FallibleIterator;
 use futures::channel::mpsc;
@@ -503,76 +501,3 @@ impl Client {
         self.inner.sender.is_closed()
     }
 }
-
-#[async_trait]
-impl GenericClient for Client {
-    async fn execute<T>(&self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<u64, Error>
-    where
-        T: ?Sized + ToStatement + Sync + Send,
-    {
-        self.execute(query, params).await
-    }
-
-    async fn execute_raw<'b, I, T>(&self, statement: &T, params: I) -> Result<u64, Error>
-    where
-        T: ?Sized + ToStatement + Sync + Send,
-        I: IntoIterator<Item = &'b dyn ToSql> + Sync + Send,
-        I::IntoIter: ExactSizeIterator,
-    {
-        self.execute_raw(statement, params).await
-    }
-
-    async fn query<T>(&self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<Vec<Row>, Error>
-    where
-        T: ?Sized + ToStatement + Sync + Send,
-    {
-        self.query(query, params).await
-    }
-
-    async fn query_one<T>(
-        &self,
-        statement: &T,
-        params: &[&(dyn ToSql + Sync)],
-    ) -> Result<Row, Error>
-    where
-        T: ?Sized + ToStatement + Sync + Send,
-    {
-        self.query_one(statement, params).await
-    }
-
-    async fn query_opt<T>(
-        &self,
-        statement: &T,
-        params: &[&(dyn ToSql + Sync)],
-    ) -> Result<Option<Row>, Error>
-    where
-        T: ?Sized + ToStatement + Sync + Send,
-    {
-        self.query_opt(statement, params).await
-    }
-
-    async fn query_raw<'b, T, I>(&self, statement: &T, params: I) -> Result<RowStream, Error>
-    where
-        T: ?Sized + ToStatement + Sync + Send,
-        I: IntoIterator<Item = &'b dyn ToSql> + Sync + Send,
-        I::IntoIter: ExactSizeIterator,
-    {
-        self.query_raw(statement, params).await
-    }
-
-    async fn prepare(&self, query: &str) -> Result<Statement, Error> {
-        self.prepare(query).await
-    }
-
-    async fn prepare_typed(
-        &self,
-        query: &str,
-        parameter_types: &[Type],
-    ) -> Result<Statement, Error> {
-        self.prepare_typed(query, parameter_types).await
-    }
-
-    async fn transaction(&mut self) -> Result<Transaction<'_>, Error> {
-        self.transaction().await
-    }
-}
diff --git a/tokio-postgres/src/generic_client.rs b/tokio-postgres/src/generic_client.rs
index cfbd83e9..30351bd0 100644
--- a/tokio-postgres/src/generic_client.rs
+++ b/tokio-postgres/src/generic_client.rs
@@ -1,11 +1,17 @@
 use crate::query::RowStream;
 use crate::types::{ToSql, Type};
-use crate::{Error, Row, Statement, ToStatement, Transaction};
+use crate::{Client, Error, Row, Statement, ToStatement, Transaction};
 use async_trait::async_trait;
 
+mod private {
+    pub trait Sealed {}
+}
+
 /// A trait allowing abstraction over connections and transactions.
+///
+/// This trait is "sealed", and cannot be implemented outside of this crate.
 #[async_trait]
-pub trait GenericClient {
+pub trait GenericClient: private::Sealed {
     /// Like `Client::execute`.
     async fn execute<T>(&self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<u64, Error>
     where
@@ -61,3 +67,154 @@ pub trait GenericClient {
     /// Like `Client::transaction`.
     async fn transaction(&mut self) -> Result<Transaction<'_>, Error>;
 }
+
+impl private::Sealed for Client {}
+
+#[async_trait]
+impl GenericClient for Client {
+    async fn execute<T>(&self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<u64, Error>
+    where
+        T: ?Sized + ToStatement + Sync + Send,
+    {
+        self.execute(query, params).await
+    }
+
+    async fn execute_raw<'b, I, T>(&self, statement: &T, params: I) -> Result<u64, Error>
+    where
+        T: ?Sized + ToStatement + Sync + Send,
+        I: IntoIterator<Item = &'b dyn ToSql> + Sync + Send,
+        I::IntoIter: ExactSizeIterator,
+    {
+        self.execute_raw(statement, params).await
+    }
+
+    async fn query<T>(&self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<Vec<Row>, Error>
+    where
+        T: ?Sized + ToStatement + Sync + Send,
+    {
+        self.query(query, params).await
+    }
+
+    async fn query_one<T>(
+        &self,
+        statement: &T,
+        params: &[&(dyn ToSql + Sync)],
+    ) -> Result<Row, Error>
+    where
+        T: ?Sized + ToStatement + Sync + Send,
+    {
+        self.query_one(statement, params).await
+    }
+
+    async fn query_opt<T>(
+        &self,
+        statement: &T,
+        params: &[&(dyn ToSql + Sync)],
+    ) -> Result<Option<Row>, Error>
+    where
+        T: ?Sized + ToStatement + Sync + Send,
+    {
+        self.query_opt(statement, params).await
+    }
+
+    async fn query_raw<'b, T, I>(&self, statement: &T, params: I) -> Result<RowStream, Error>
+    where
+        T: ?Sized + ToStatement + Sync + Send,
+        I: IntoIterator<Item = &'b dyn ToSql> + Sync + Send,
+        I::IntoIter: ExactSizeIterator,
+    {
+        self.query_raw(statement, params).await
+    }
+
+    async fn prepare(&self, query: &str) -> Result<Statement, Error> {
+        self.prepare(query).await
+    }
+
+    async fn prepare_typed(
+        &self,
+        query: &str,
+        parameter_types: &[Type],
+    ) -> Result<Statement, Error> {
+        self.prepare_typed(query, parameter_types).await
+    }
+
+    async fn transaction(&mut self) -> Result<Transaction<'_>, Error> {
+        self.transaction().await
+    }
+}
+
+impl private::Sealed for Transaction<'_> {}
+
+#[async_trait]
+impl GenericClient for Transaction<'_> {
+    async fn execute<T>(&self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<u64, Error>
+    where
+        T: ?Sized + ToStatement + Sync + Send,
+    {
+        self.execute(query, params).await
+    }
+
+    async fn execute_raw<'b, I, T>(&self, statement: &T, params: I) -> Result<u64, Error>
+    where
+        T: ?Sized + ToStatement + Sync + Send,
+        I: IntoIterator<Item = &'b dyn ToSql> + Sync + Send,
+        I::IntoIter: ExactSizeIterator,
+    {
+        self.execute_raw(statement, params).await
+    }
+
+    async fn query<T>(&self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<Vec<Row>, Error>
+    where
+        T: ?Sized + ToStatement + Sync + Send,
+    {
+        self.query(query, params).await
+    }
+
+    async fn query_one<T>(
+        &self,
+        statement: &T,
+        params: &[&(dyn ToSql + Sync)],
+    ) -> Result<Row, Error>
+    where
+        T: ?Sized + ToStatement + Sync + Send,
+    {
+        self.query_one(statement, params).await
+    }
+
+    async fn query_opt<T>(
+        &self,
+        statement: &T,
+        params: &[&(dyn ToSql + Sync)],
+    ) -> Result<Option<Row>, Error>
+    where
+        T: ?Sized + ToStatement + Sync + Send,
+    {
+        self.query_opt(statement, params).await
+    }
+
+    async fn query_raw<'b, T, I>(&self, statement: &T, params: I) -> Result<RowStream, Error>
+    where
+        T: ?Sized + ToStatement + Sync + Send,
+        I: IntoIterator<Item = &'b dyn ToSql> + Sync + Send,
+        I::IntoIter: ExactSizeIterator,
+    {
+        self.query_raw(statement, params).await
+    }
+
+    async fn prepare(&self, query: &str) -> Result<Statement, Error> {
+        self.prepare(query).await
+    }
+
+    async fn prepare_typed(
+        &self,
+        query: &str,
+        parameter_types: &[Type],
+    ) -> Result<Statement, Error> {
+        self.prepare_typed(query, parameter_types).await
+    }
+
+    #[allow(clippy::needless_lifetimes)]
+    async fn transaction<'a>(&'a mut self) -> Result<Transaction<'a>, Error> {
+        self.transaction().await
+    }
+}
diff --git a/tokio-postgres/src/transaction.rs b/tokio-postgres/src/transaction.rs
index c7508737..a1ee4f6c 100644
--- a/tokio-postgres/src/transaction.rs
+++ b/tokio-postgres/src/transaction.rs
@@ -12,7 +12,6 @@ use crate::{
     bind, query, slice_iter, CancelToken, Client, CopyInSink, Error, Portal, Row,
     SimpleQueryMessage, Statement, ToStatement,
 };
-use async_trait::async_trait;
 use bytes::Buf;
 use futures::TryStreamExt;
 use postgres_protocol::message::frontend;
@@ -286,77 +285,3 @@ impl<'a> Transaction<'a> {
         })
     }
 }
-
-#[async_trait]
-impl crate::GenericClient for Transaction<'_> {
-    async fn execute<T>(&self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<u64, Error>
-    where
-        T: ?Sized + ToStatement + Sync + Send,
-    {
-        self.execute(query, params).await
-    }
-
-    async fn execute_raw<'b, I, T>(&self, statement: &T, params: I) -> Result<u64, Error>
-    where
-        T: ?Sized + ToStatement + Sync + Send,
-        I: IntoIterator<Item = &'b dyn ToSql> + Sync + Send,
-        I::IntoIter: ExactSizeIterator,
-    {
-        self.execute_raw(statement, params).await
-    }
-
-    async fn query<T>(&self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<Vec<Row>, Error>
-    where
-        T: ?Sized + ToStatement + Sync + Send,
-    {
-        self.query(query, params).await
-    }
-
-    async fn query_one<T>(
-        &self,
-        statement: &T,
-        params: &[&(dyn ToSql + Sync)],
-    ) -> Result<Row, Error>
-    where
-        T: ?Sized + ToStatement + Sync + Send,
-    {
-        self.query_one(statement, params).await
-    }
-
-    async fn query_opt<T>(
-        &self,
-        statement: &T,
-        params: &[&(dyn ToSql + Sync)],
-    ) -> Result<Option<Row>, Error>
-    where
-        T: ?Sized + ToStatement + Sync + Send,
-    {
-        self.query_opt(statement, params).await
-    }
-
-    async fn query_raw<'b, T, I>(&self, statement: &T, params: I) -> Result<RowStream, Error>
-    where
-        T: ?Sized + ToStatement + Sync + Send,
-        I: IntoIterator<Item = &'b dyn ToSql> + Sync + Send,
-        I::IntoIter: ExactSizeIterator,
-    {
-        self.query_raw(statement, params).await
-    }
-
-    async fn prepare(&self, query: &str) -> Result<Statement, Error> {
-        self.prepare(query).await
-    }
-
-    async fn prepare_typed(
-        &self,
-        query: &str,
-        parameter_types: &[Type],
-    ) -> Result<Statement, Error> {
-        self.prepare_typed(query, parameter_types).await
-    }
-
-    #[allow(clippy::needless_lifetimes)]
-    async fn transaction<'a>(&'a mut self) -> Result<Transaction<'a>, Error> {
-        self.transaction().await
-    }
-}