diff --git a/src/lib.rs b/src/lib.rs
index 1cdd426..6471dd0 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -49,10 +49,10 @@
     unused_extern_crates,
     unused_qualifications
 )]
-#![cfg_attr(not(test), no_std)]
+#![no_std]
 
 extern crate alloc;
-#[cfg(all(feature = "std", not(test)))]
+#[cfg(any(feature = "std", test))]
 extern crate std;
 
 #[cfg(test)]
diff --git a/src/pemfile.rs b/src/pemfile.rs
index f633204..2fe209c 100644
--- a/src/pemfile.rs
+++ b/src/pemfile.rs
@@ -215,14 +215,8 @@ fn read_one_impl(
     }
 
     if section.is_some() {
-        let mut trim = 0;
-        for &b in line.iter().rev() {
-            match b {
-                b'\n' | b'\r' | b' ' => trim += 1,
-                _ => break,
-            }
-        }
-        b64buf.extend(&line[..line.len() - trim]);
+        // Extend b64buf without leading or trailing whitespace
+        b64buf.extend(trim_ascii(line));
     }
 
     Ok(ControlFlow::Continue(()))
@@ -266,6 +260,35 @@ fn read_until_newline<R: io::BufRead + ?Sized>(
     }
 }
 
+/// Trim contiguous leading and trailing whitespace from `line`.
+///
+/// We use [u8::is_ascii_whitespace] to determine what is whitespace.
+// TODO(XXX): Replace with `[u8]::trim_ascii` once stabilized[0] and available in our MSRV.
+//   [0]: https://github.com/rust-lang/rust/issues/94035
+const fn trim_ascii(line: &[u8]) -> &[u8] {
+    let mut bytes = line;
+
+    // Note: A pattern matching based approach (instead of indexing) allows
+    // making the function const.
+    while let [first, rest @ ..] = bytes {
+        if first.is_ascii_whitespace() {
+            bytes = rest;
+        } else {
+            break;
+        }
+    }
+
+    while let [rest @ .., last] = bytes {
+        if last.is_ascii_whitespace() {
+            bytes = rest;
+        } else {
+            break;
+        }
+    }
+
+    bytes
+}
+
 /// Extract and return all PEM sections by reading `rd`.
 #[cfg(feature = "std")]
 pub fn read_all(rd: &mut dyn io::BufRead) -> impl Iterator<Item = Result<Item, io::Error>> + '_ {
@@ -284,3 +307,31 @@ mod base64 {
     );
 }
 use self::base64::Engine;
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn test_trim_ascii() {
+        let tests: &[(&[u8], &[u8])] = &[
+            (b"", b""),
+            (b"   hello world   ", b"hello world"),
+            (b"   hello\t\r\nworld   ", b"hello\t\r\nworld"),
+            (b"\n\r  \ttest\t  \r\n", b"test"),
+            (b"   \r\n  ", b""),
+            (b"no trimming needed", b"no trimming needed"),
+            (
+                b"\n\n content\n\n more content\n\n",
+                b"content\n\n more content",
+            ),
+        ];
+
+        for &(input, expected) in tests {
+            assert_eq!(
+                super::trim_ascii(input),
+                expected,
+                "Failed for input: {:?}",
+                input,
+            );
+        }
+    }
+}
diff --git a/src/tests.rs b/src/tests.rs
index 3c32998..290f89b 100644
--- a/src/tests.rs
+++ b/src/tests.rs
@@ -1,5 +1,8 @@
 #[cfg(test)]
 mod unit {
+    use alloc::{format, vec};
+    use std::prelude::v1::*;
+
     use crate::{Error, Item};
 
     #[test]
diff --git a/tests/data/whitespace-prefix.crt b/tests/data/whitespace-prefix.crt
new file mode 100644
index 0000000..227fa8a
--- /dev/null
+++ b/tests/data/whitespace-prefix.crt
@@ -0,0 +1,21 @@
+-----BEGIN CERTIFICATE-----
+ MIIDaTCCAlGgAwIBAgIJAOq/zL+84IswMA0GCSqGSIb3DQEBCwUAMFoxCzAJBgNV
+ BAYTAlVTMQswCQYDVQQIDAJOQzEMMAoGA1UEBwwDUlRQMQ8wDQYDVQQKDAZOZXRB
+ cHAxDTALBgNVBAsMBEVTSVMxEDAOBgNVBAMMB1NTRk1DQ0EwHhcNMTcxMTAxMjEw
+ OTQyWhcNMjcxMDMwMjEwOTQyWjBaMQswCQYDVQQGEwJVUzELMAkGA1UECAwCTkMx
+ DDAKBgNVBAcMA1JUUDEPMA0GA1UECgwGTmV0QXBwMQ0wCwYDVQQLDARFU0lTMRAw
+ DgYDVQQDDAdTU0ZNQ0NBMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA
+ iaD9Ee0Yrdka0I+9GTJBIW/Fp5JU6kyjaxfOldW/R9lEubegXQFhDD2Xi1HZ+fTM
+ f224glB9xLJXAHhipRK01C2MgC4kSH75WL1iAiYeOBloExqmK6OCX+sdyO7RXm/H
+ Ra9tN2INWdvyO2pnmxsSnq56mCMsUZLtrRKp89FWgcxLg5r8QxH7xwfh5k54rxjE
+ 144TD9yrIiQOgRSIRHUrVJ9l/F/gnwzP8wcNABeXwN71Mzl7mliPA703kONQIAyU
+ 0E0tLpmy/U8dZdMmTBZGB7jI9f95Hl1RunfwhR371a6z38kgkvwrLzl4qflfsPjw
+ K9n4omNk9rCH9H9tWkxxjwIDAQABozIwMDAdBgNVHQ4EFgQU/bFyCCnqdDFKlQBJ
+ ExtV6wcMYkEwDwYDVR0TAQH/BAUwAwEB/zANBgkqhkiG9w0BAQsFAAOCAQEAOQMs
+ Pz2iBD1+3RcSOsahB36WAwPCjgPiXXXpU+Zri11+m6I0Lq+OWtf+YgaQ8ylLmCQd
+ 0p1wHlYA4qo896SycrhTQfy9GlS/aQqN192k3oBGoJcMIUnGUBGuEvyZ2aDUfkzy
+ JUqBe+0KaT7pkvvbRL7VUz34I7ouq9fQIRZ26vUDLTY3KM1n/DXBj3e30GHGMV3K
+ NN2twuLXPNjnryfgpliHU1rwV7r1WvrCVn4StjimP2bO5HGqD/SbiYUL2M9LOuLK
+ 6mqY4OHumYXq3k7CHrvt0FepsN0L14LYEt1LvpPDFWP3SdN4z4KqT9AGqBaJnhhl
+ Qiq8GWnAChspdBLxCg==
+-----END CERTIFICATE-----
diff --git a/tests/integration.rs b/tests/integration.rs
index 27d5b9c..d9620ff 100644
--- a/tests/integration.rs
+++ b/tests/integration.rs
@@ -196,3 +196,15 @@ fn different_line_endings() {
         assert!(matches!(cert, rustls_pemfile::Item::X509Certificate(_)));
     }
 }
+
+#[test]
+fn whitespace_prefix() {
+    let items = rustls_pemfile::read_all(&mut BufReader::new(
+        &include_bytes!("data/whitespace-prefix.crt")[..],
+    ))
+    .collect::<Result<Vec<_>, _>>()
+    .unwrap();
+
+    assert_eq!(items.len(), 1);
+    assert!(matches!(items[0], rustls_pemfile::Item::X509Certificate(_)));
+}