diff --git a/tokio-postgres/src/client.rs b/tokio-postgres/src/client.rs
index f87e11ba..96e724d4 100644
--- a/tokio-postgres/src/client.rs
+++ b/tokio-postgres/src/client.rs
@@ -507,7 +507,7 @@ impl Client {
 #[async_trait]
 impl GenericClient for Client {
     /// Like `Client::execute`.
-    async fn execute<T>(&mut self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<u64, Error>
+    async fn execute<T>(&self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<u64, Error>
     where
         T: ?Sized + ToStatement + Sync + Send,
     {
@@ -525,11 +525,7 @@ impl GenericClient for Client {
     }
 
     /// Like `Client::query`.
-    async fn query<T>(
-        &mut self,
-        query: &T,
-        params: &[&(dyn ToSql + Sync)],
-    ) -> Result<Vec<Row>, Error>
+    async fn query<T>(&self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<Vec<Row>, Error>
     where
         T: ?Sized + ToStatement + Sync + Send,
     {
@@ -571,7 +567,7 @@ impl GenericClient for Client {
     }
 
     /// Like `Client::prepare`.
-    async fn prepare(&mut self, query: &str) -> Result<Statement, Error> {
+    async fn prepare(&self, query: &str) -> Result<Statement, Error> {
         self.prepare(query).await
     }
 
diff --git a/tokio-postgres/src/generic_client.rs b/tokio-postgres/src/generic_client.rs
index 53473737..cfbd83e9 100644
--- a/tokio-postgres/src/generic_client.rs
+++ b/tokio-postgres/src/generic_client.rs
@@ -7,7 +7,7 @@ use async_trait::async_trait;
 #[async_trait]
 pub trait GenericClient {
     /// Like `Client::execute`.
-    async fn execute<T>(&mut self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<u64, Error>
+    async fn execute<T>(&self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<u64, Error>
     where
         T: ?Sized + ToStatement + Sync + Send;
 
@@ -19,11 +19,7 @@ pub trait GenericClient {
         I::IntoIter: ExactSizeIterator;
 
     /// Like `Client::query`.
-    async fn query<T>(
-        &mut self,
-        query: &T,
-        params: &[&(dyn ToSql + Sync)],
-    ) -> Result<Vec<Row>, Error>
+    async fn query<T>(&self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<Vec<Row>, Error>
     where
         T: ?Sized + ToStatement + Sync + Send;
 
@@ -53,7 +49,7 @@ pub trait GenericClient {
         I::IntoIter: ExactSizeIterator;
 
     /// Like `Client::prepare`.
-    async fn prepare(&mut self, query: &str) -> Result<Statement, Error>;
+    async fn prepare(&self, query: &str) -> Result<Statement, Error>;
 
     /// Like `Client::prepare_typed`.
     async fn prepare_typed(
diff --git a/tokio-postgres/src/transaction.rs b/tokio-postgres/src/transaction.rs
index b165cbed..6d02ec52 100644
--- a/tokio-postgres/src/transaction.rs
+++ b/tokio-postgres/src/transaction.rs
@@ -290,7 +290,7 @@ impl<'a> Transaction<'a> {
 #[async_trait]
 impl crate::GenericClient for Transaction<'_> {
     /// Like `Transaction::execute`.
-    async fn execute<T>(&mut self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<u64, Error>
+    async fn execute<T>(&self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<u64, Error>
     where
         T: ?Sized + ToStatement + Sync + Send,
     {
@@ -308,11 +308,7 @@ impl crate::GenericClient for Transaction<'_> {
     }
 
     /// Like `Transaction::query`.
-    async fn query<T>(
-        &mut self,
-        query: &T,
-        params: &[&(dyn ToSql + Sync)],
-    ) -> Result<Vec<Row>, Error>
+    async fn query<T>(&self, query: &T, params: &[&(dyn ToSql + Sync)]) -> Result<Vec<Row>, Error>
     where
         T: ?Sized + ToStatement + Sync + Send,
     {
@@ -354,7 +350,7 @@ impl crate::GenericClient for Transaction<'_> {
     }
 
     /// Like `Transaction::prepare`.
-    async fn prepare(&mut self, query: &str) -> Result<Statement, Error> {
+    async fn prepare(&self, query: &str) -> Result<Statement, Error> {
         self.prepare(query).await
     }