diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 0d24d01..10ba00d 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -11,7 +11,7 @@ jobs:
         rust:
           - stable
           - beta
-          - 1.40.0
+          - 1.45.2
     steps:
       - uses: actions/checkout@v1
       - uses: actions-rs/toolchain@v1
@@ -37,7 +37,6 @@ jobs:
           args: --no-default-features --features=builder,smtp-transport,file-transport,sendmail-transport
       - run: rm target/debug/deps/liblettre-*
       - uses: actions-rs/cargo@v1
-        if: matrix.rust != '1.40.0'
         with:
           command: test
           args: --features=async-std1
@@ -54,7 +53,7 @@ jobs:
         rust:
           - stable
           - beta
-          - 1.40.0
+          - 1.45.2
     steps:
       - uses: actions/checkout@v1
       - uses: actions-rs/toolchain@v1
diff --git a/README.md b/README.md
index 0de29d5..4373967 100644
--- a/README.md
+++ b/README.md
@@ -53,7 +53,7 @@ Lettre does not provide (for now):
 
 ## Example
 
-This library requires Rust 1.40 or newer.
+This library requires Rust 1.45 or newer.
 To use this library, add the following to your `Cargo.toml`:
 
 
diff --git a/src/message/utf8_b.rs b/src/message/utf8_b.rs
index e1b347f..ae6d78e 100644
--- a/src/message/utf8_b.rs
+++ b/src/message/utf8_b.rs
@@ -16,19 +16,16 @@ pub fn encode(s: &str) -> String {
 }
 
 pub fn decode(s: &str) -> Option<String> {
-    const PREFIX: &str = "=?utf-8?b?";
-    const SUFFIX: &str = "?=";
-
-    let s = s.trim();
-    if s.starts_with(PREFIX) && s.ends_with(SUFFIX) {
-        let s = &s[PREFIX.len()..];
-        let s = &s[..s.len() - SUFFIX.len()];
-        base64::decode(s)
-            .ok()
-            .and_then(|v| String::from_utf8(v).ok())
-    } else {
-        Some(s.into())
-    }
+    s.strip_prefix("=?utf-8?b?")
+        .and_then(|stripped| stripped.strip_suffix("?="))
+        .map_or_else(
+            || Some(s.into()),
+            |stripped| {
+                let decoded = base64::decode(stripped).ok()?;
+                let decoded = String::from_utf8(decoded).ok()?;
+                Some(decoded)
+            },
+        )
 }
 
 #[cfg(test)]
diff --git a/src/transport/smtp/response.rs b/src/transport/smtp/response.rs
index bd20145..c346715 100644
--- a/src/transport/smtp/response.rs
+++ b/src/transport/smtp/response.rs
@@ -151,10 +151,10 @@ impl Response {
 
     /// Tells if the response is positive
     pub fn is_positive(&self) -> bool {
-        match self.code.severity {
-            Severity::PositiveCompletion | Severity::PositiveIntermediate => true,
-            _ => false,
-        }
+        matches!(
+            self.code.severity,
+            Severity::PositiveCompletion | Severity::PositiveIntermediate
+        )
     }
 
     /// Tests code equality