diff --git a/crates/stdlib/src/base64.rs b/crates/stdlib/src/base64.rs
new file mode 100644
index 0000000000..e98ff24058
--- /dev/null
+++ b/crates/stdlib/src/base64.rs
@@ -0,0 +1,90 @@
+// Base64 encoding module
+
+pub(crate) use _base64::make_module;
+
+const PAD_BYTE: u8 = b'=';
+const ENCODE_TABLE: &[u8; 64] = b"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+
+#[inline]
+fn encoded_output_len(input_len: usize) -> Option<usize> {
+    input_len
+        .checked_add(2)
+        .map(|n| n / 3)
+        .and_then(|blocks| blocks.checked_mul(4))
+}
+
+#[inline]
+fn encode_into(input: &[u8], output: &mut [u8]) -> usize {
+    let mut src_index = 0;
+    let mut dst_index = 0;
+    let len = input.len();
+
+    // Process full 3-byte chunks
+    while src_index + 3 <= len {
+        let chunk = (u32::from(input[src_index]) << 16)
+            | (u32::from(input[src_index + 1]) << 8)
+            | u32::from(input[src_index + 2]);
+        output[dst_index] = ENCODE_TABLE[((chunk >> 18) & 0x3f) as usize];
+        output[dst_index + 1] = ENCODE_TABLE[((chunk >> 12) & 0x3f) as usize];
+        output[dst_index + 2] = ENCODE_TABLE[((chunk >> 6) & 0x3f) as usize];
+        output[dst_index + 3] = ENCODE_TABLE[(chunk & 0x3f) as usize];
+        src_index += 3;
+        dst_index += 4;
+    }
+
+    // Process remaining bytes (1 or 2 bytes)
+    match len - src_index {
+        0 => {}
+        1 => {
+            let chunk = u32::from(input[src_index]) << 16;
+            output[dst_index] = ENCODE_TABLE[((chunk >> 18) & 0x3f) as usize];
+            output[dst_index + 1] = ENCODE_TABLE[((chunk >> 12) & 0x3f) as usize];
+            output[dst_index + 2] = PAD_BYTE;
+            output[dst_index + 3] = PAD_BYTE;
+            dst_index += 4;
+        }
+        2 => {
+            let chunk =
+                (u32::from(input[src_index]) << 16) | (u32::from(input[src_index + 1]) << 8);
+            output[dst_index] = ENCODE_TABLE[((chunk >> 18) & 0x3f) as usize];
+            output[dst_index + 1] = ENCODE_TABLE[((chunk >> 12) & 0x3f) as usize];
+            output[dst_index + 2] = ENCODE_TABLE[((chunk >> 6) & 0x3f) as usize];
+            output[dst_index + 3] = PAD_BYTE;
+            dst_index += 4;
+        }
+        _ => unreachable!("len - src_index cannot exceed 2"),
+    }
+
+    dst_index
+}
+
+#[pymodule(name = "_base64")]
+mod _base64 {
+    use rustpython_vm::builtins::PyBytes;
+
+    use crate::vm::{PyResult, VirtualMachine, function::ArgBytesLike};
+
+    // argument is parsed by #[pyfunction]. It replaces clinic.
+    #[pyfunction]
+    fn standard_b64encode(data: ArgBytesLike, vm: &VirtualMachine) -> PyResult<PyBytes> {
+        data.with_ref(|input| {
+            let input_len = input.len();
+
+            // input len can't be negative in RustPython
+
+            let Some(output_len) = super::encoded_output_len(input_len) else {
+                return Err(vm.new_memory_error("output length overflow".to_owned()));
+            };
+
+            if output_len > isize::MAX as usize {
+                return Err(vm.new_memory_error("output too large".to_owned()));
+            }
+
+            let mut output = vec![0u8; output_len];
+            let written = super::encode_into(input, &mut output);
+            debug_assert_eq!(written, output_len);
+
+            Ok(PyBytes::from(output))
+        })
+    }
+}
diff --git a/crates/stdlib/src/lib.rs b/crates/stdlib/src/lib.rs
index 01a27b7660..624d697ad7 100644
--- a/crates/stdlib/src/lib.rs
+++ b/crates/stdlib/src/lib.rs
@@ -8,6 +8,7 @@
 extern crate rustpython_derive;
 
 pub mod array;
+mod base64;
 mod binascii;
 mod bisect;
 mod cmath;
@@ -123,6 +124,7 @@ pub fn get_module_inits() -> impl Iterator<Item = (Cow<'static, str>, StdlibInit
         #[cfg(all())]
         {
             "array" => array::make_module,
+            "_base64" => base64::make_module,
             "binascii" => binascii::make_module,
             "_bisect" => bisect::make_module,
             "_bz2" => bz2::make_module,