diff --git a/Cargo.lock b/Cargo.lock
index 6c30a182d..3633928c6 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1064,6 +1064,15 @@ version = "2.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b16bd47d9e329435e309c58469fe0791c2d0d1ba96ec0954152a5ae2b04387dc"
 
+[[package]]
+name = "memmap2"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4647a11b578fead29cdbb34d4adef8dd3dc35b876c9c6d5240d83f205abfe96e"
+dependencies = [
+ "libc",
+]
+
 [[package]]
 name = "memoffset"
 version = "0.6.4"
@@ -3025,6 +3034,7 @@ version = "0.0.7"
 dependencies = [
  "clap",
  "memchr 2.4.0",
+ "memmap2",
  "regex",
  "uucore",
  "uucore_procs",
diff --git a/src/uu/tac/Cargo.toml b/src/uu/tac/Cargo.toml
index 1e436e916..00803c8d2 100644
--- a/src/uu/tac/Cargo.toml
+++ b/src/uu/tac/Cargo.toml
@@ -1,3 +1,5 @@
+# spell-checker:ignore memmap
+
 [package]
 name = "uu_tac"
 version = "0.0.7"
@@ -16,6 +18,7 @@ path = "src/tac.rs"
 
 [dependencies]
 memchr = "2"
+memmap2 = "0.5"
 regex = "1"
 clap = { version = "2.33", features = ["wrap_help"] }
 uucore = { version=">=0.0.9", package="uucore", path="../../uucore" }
diff --git a/src/uu/tac/src/tac.rs b/src/uu/tac/src/tac.rs
index 370e92230..cdb2d74e3 100644
--- a/src/uu/tac/src/tac.rs
+++ b/src/uu/tac/src/tac.rs
@@ -5,15 +5,19 @@
 //  * For the full copyright and license information, please view the LICENSE
 //  * file that was distributed with this source code.
 
-// spell-checker:ignore (ToDO) sbytes slen dlen memmem
+// spell-checker:ignore (ToDO) sbytes slen dlen memmem memmap Mmap mmap SIGBUS
 
 #[macro_use]
 extern crate uucore;
 
 use clap::{crate_version, App, Arg};
 use memchr::memmem;
+use memmap2::Mmap;
 use std::io::{stdin, stdout, BufWriter, Read, Write};
-use std::{fs::read, path::Path};
+use std::{
+    fs::{read, File},
+    path::Path,
+};
 use uucore::display::Quotable;
 use uucore::InvalidEncodingHandling;
 
@@ -220,14 +224,23 @@ fn tac(filenames: Vec<&str>, before: bool, regex: bool, separator: &str) -> i32
     };
 
     for &filename in &filenames {
-        let data = if filename == "-" {
-            let mut data = Vec::new();
-            if let Err(e) = stdin().read_to_end(&mut data) {
-                show_error!("failed to read from stdin: {}", e);
-                exit_code = 1;
-                continue;
+        let mmap;
+        let buf;
+
+        let data: &[u8] = if filename == "-" {
+            if let Some(mmap1) = try_mmap_stdin() {
+                mmap = mmap1;
+                &mmap
+            } else {
+                let mut buf1 = Vec::new();
+                if let Err(e) = stdin().read_to_end(&mut buf1) {
+                    show_error!("failed to read from stdin: {}", e);
+                    exit_code = 1;
+                    continue;
+                }
+                buf = buf1;
+                &buf
             }
-            data
         } else {
             let path = Path::new(filename);
             if path.is_dir() || path.metadata().is_err() {
@@ -242,22 +255,47 @@ fn tac(filenames: Vec<&str>, before: bool, regex: bool, separator: &str) -> i32
                 exit_code = 1;
                 continue;
             }
-            match read(path) {
-                Ok(data) => data,
-                Err(e) => {
-                    show_error!("failed to read {}: {}", filename.quote(), e);
-                    exit_code = 1;
-                    continue;
+
+            if let Some(mmap1) = try_mmap_path(path) {
+                mmap = mmap1;
+                &mmap
+            } else {
+                match read(path) {
+                    Ok(buf1) => {
+                        buf = buf1;
+                        &buf
+                    }
+                    Err(e) => {
+                        show_error!("failed to read {}: {}", filename.quote(), e);
+                        exit_code = 1;
+                        continue;
+                    }
                 }
             }
         };
 
         if let Some(pattern) = &pattern {
-            buffer_tac_regex(&data, pattern, before)
+            buffer_tac_regex(data, pattern, before)
         } else {
-            buffer_tac(&data, before, separator)
+            buffer_tac(data, before, separator)
         }
         .unwrap_or_else(|e| crash!(1, "failed to write to stdout: {}", e));
     }
     exit_code
 }
+
+fn try_mmap_stdin() -> Option<Mmap> {
+    // SAFETY: If the file is truncated while we map it, SIGBUS will be raised
+    // and our process will be terminated, thus preventing access of invalid memory.
+    unsafe { Mmap::map(&stdin()).ok() }
+}
+
+fn try_mmap_path(path: &Path) -> Option<Mmap> {
+    let file = File::open(path).ok()?;
+
+    // SAFETY: If the file is truncated while we map it, SIGBUS will be raised
+    // and our process will be terminated, thus preventing access of invalid memory.
+    let mmap = unsafe { Mmap::map(&file).ok()? };
+
+    Some(mmap)
+}