diff --git a/README.md b/README.md
index 77e7272..7513666 100644
--- a/README.md
+++ b/README.md
@@ -19,7 +19,7 @@ use std::path::PathBuf;
 
 fn main() {
     let path = setup();
-    let mut database = sqlite::open(&path).unwrap();
+    let database = sqlite::open(&path).unwrap();
 
     database.execute(r#"
         CREATE TABLE `users` (id INTEGER, name VARCHAR(255));
diff --git a/examples/workflow.rs b/examples/workflow.rs
index 5e807d4..87597a9 100644
--- a/examples/workflow.rs
+++ b/examples/workflow.rs
@@ -4,7 +4,7 @@ use std::path::PathBuf;
 
 fn main() {
     let path = setup();
-    let mut database = sqlite::open(&path).unwrap();
+    let database = sqlite::open(&path).unwrap();
 
     database.execute(r#"
         CREATE TABLE `users` (id INTEGER, name VARCHAR(255));
diff --git a/src/database.rs b/src/database.rs
index 184ef55..91abd0a 100644
--- a/src/database.rs
+++ b/src/database.rs
@@ -25,8 +25,8 @@ impl Database {
     }
 
     /// Execute an SQL statement.
-    pub fn execute<'l>(&mut self, sql: &str,
-                       callback: Option<&mut ExecuteCallback<'l>>) -> Result<()> {
+    pub fn execute<'l>(&self, sql: &str, callback: Option<&mut ExecuteCallback<'l>>)
+                      -> Result<()> {
 
         unsafe {
             match callback {
@@ -49,7 +49,7 @@ impl Database {
 
     /// Create a prepared statement.
     #[inline]
-    pub fn statement<'l>(&'l mut self, sql: &str) -> Result<Statement<'l>> {
+    pub fn statement<'l>(&'l self, sql: &str) -> Result<Statement<'l>> {
         ::statement::new(self, sql)
     }
 }
@@ -62,7 +62,7 @@ impl Drop for Database {
 }
 
 #[inline]
-pub fn as_raw(database: &mut Database) -> *mut raw::sqlite3 {
+pub fn as_raw(database: &Database) -> *mut raw::sqlite3 {
     database.raw
 }
 
diff --git a/src/error.rs b/src/error.rs
index ba23143..93661ea 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -13,7 +13,7 @@ pub struct Error {
 
 impl Error {
     /// Return the last occurred error if any.
-    pub fn last(database: &mut Database) -> Option<Error> {
+    pub fn last(database: &Database) -> Option<Error> {
         unsafe {
             let code = raw::sqlite3_errcode(::database::as_raw(database));
             if code == raw::SQLITE_OK {
diff --git a/src/statement.rs b/src/statement.rs
index f2b9b0f..e10e0e3 100644
--- a/src/statement.rs
+++ b/src/statement.rs
@@ -101,7 +101,7 @@ impl Value for String {
 }
 
 #[inline]
-pub fn new<'l>(database: &'l mut Database, sql: &str) -> Result<Statement<'l>> {
+pub fn new<'l>(database: &'l Database, sql: &str) -> Result<Statement<'l>> {
     let mut raw = 0 as *mut _;
     unsafe {
         success!(database, raw::sqlite3_prepare(::database::as_raw(database), str_to_c_str!(sql),
diff --git a/tests/lib.rs b/tests/lib.rs
index 83e0bf5..08a11f1 100644
--- a/tests/lib.rs
+++ b/tests/lib.rs
@@ -18,7 +18,7 @@ fn workflow() {
     );
 
     let (path, _directory) = setup();
-    let mut database = ok!(sqlite::open(&path));
+    let database = ok!(sqlite::open(&path));
 
     let sql = r#"CREATE TABLE `users` (id INTEGER, name VARCHAR(255), age REAL);"#;
     ok!(database.execute(sql, None));
@@ -58,7 +58,7 @@ fn workflow() {
 #[test]
 fn failure() {
     let (path, _directory) = setup();
-    let mut database = ok!(sqlite::open(&path));
+    let database = ok!(sqlite::open(&path));
     match database.execute(":)", None) {
         Err(error) => assert_eq!(error.message, Some(String::from(r#"unrecognized token: ":""#))),
         _ => assert!(false),