diff --git a/src/tools/miri/README.md b/src/tools/miri/README.md
index 48581f6bbff..9bd8ed1c499 100644
--- a/src/tools/miri/README.md
+++ b/src/tools/miri/README.md
@@ -590,7 +590,7 @@ extern "Rust" {
     /// `out` must point to at least `out_size` many bytes, and the result will be stored there
     /// with a null terminator.
     /// Returns 0 if the `out` buffer was large enough, and the required size otherwise.
-    fn miri_host_to_target_path(path: *const i8, out: *mut i8, out_size: usize) -> usize;
+    fn miri_host_to_target_path(path: *const c_char, out: *mut c_char, out_size: usize) -> usize;
 }
 ```
 
diff --git a/src/tools/miri/test-cargo-miri/src/main.rs b/src/tools/miri/test-cargo-miri/src/main.rs
index 048dbbbaa0f..048577ef15a 100644
--- a/src/tools/miri/test-cargo-miri/src/main.rs
+++ b/src/tools/miri/test-cargo-miri/src/main.rs
@@ -23,7 +23,7 @@ fn main() {
     // (We rely on the test runner to always disable isolation when passing no arguments.)
     if std::env::args().len() <= 1 {
         fn host_to_target_path(path: String) -> PathBuf {
-            use std::ffi::{CStr, CString};
+            use std::ffi::{c_char, CStr, CString};
 
             let path = CString::new(path).unwrap();
             let mut out = Vec::with_capacity(1024);
@@ -31,8 +31,8 @@ fn main() {
             unsafe {
                 extern "Rust" {
                     fn miri_host_to_target_path(
-                        path: *const i8,
-                        out: *mut i8,
+                        path: *const c_char,
+                        out: *mut c_char,
                         out_size: usize,
                     ) -> usize;
                 }
diff --git a/src/tools/miri/test-cargo-miri/subcrate/main.rs b/src/tools/miri/test-cargo-miri/subcrate/main.rs
index 1cb8091f877..52161098788 100644
--- a/src/tools/miri/test-cargo-miri/subcrate/main.rs
+++ b/src/tools/miri/test-cargo-miri/subcrate/main.rs
@@ -5,7 +5,7 @@ fn main() {
     println!("subcrate running");
 
     fn host_to_target_path(path: String) -> PathBuf {
-        use std::ffi::{CStr, CString};
+        use std::ffi::{c_char, CStr, CString};
 
         let path = CString::new(path).unwrap();
         let mut out = Vec::with_capacity(1024);
@@ -13,8 +13,8 @@ fn main() {
         unsafe {
             extern "Rust" {
                 fn miri_host_to_target_path(
-                    path: *const i8,
-                    out: *mut i8,
+                    path: *const c_char,
+                    out: *mut c_char,
                     out_size: usize,
                 ) -> usize;
             }
diff --git a/src/tools/miri/test-cargo-miri/subcrate/test.rs b/src/tools/miri/test-cargo-miri/subcrate/test.rs
index 619d8c72fd0..1681c721dc2 100644
--- a/src/tools/miri/test-cargo-miri/subcrate/test.rs
+++ b/src/tools/miri/test-cargo-miri/subcrate/test.rs
@@ -8,7 +8,7 @@ fn main() {
     println!("subcrate testing");
 
     fn host_to_target_path(path: String) -> PathBuf {
-        use std::ffi::{CStr, CString};
+        use std::ffi::{c_char, CStr, CString};
 
         let path = CString::new(path).unwrap();
         let mut out = Vec::with_capacity(1024);
@@ -16,8 +16,8 @@ fn main() {
         unsafe {
             extern "Rust" {
                 fn miri_host_to_target_path(
-                    path: *const i8,
-                    out: *mut i8,
+                    path: *const c_char,
+                    out: *mut c_char,
                     out_size: usize,
                 ) -> usize;
             }
diff --git a/src/tools/miri/tests/pass-dep/shims/libc-fs.rs b/src/tools/miri/tests/pass-dep/shims/libc-fs.rs
index ba5b269f652..cd071a7f32a 100644
--- a/src/tools/miri/tests/pass-dep/shims/libc-fs.rs
+++ b/src/tools/miri/tests/pass-dep/shims/libc-fs.rs
@@ -5,7 +5,7 @@
 #![feature(io_error_uncategorized)]
 
 use std::convert::TryInto;
-use std::ffi::{CStr, CString};
+use std::ffi::{c_char, CStr, CString};
 use std::fs::{canonicalize, remove_dir_all, remove_file, File};
 use std::io::{Error, ErrorKind, Write};
 use std::os::unix::ffi::OsStrExt;
@@ -31,7 +31,11 @@ fn tmp() -> PathBuf {
 
     unsafe {
         extern "Rust" {
-            fn miri_host_to_target_path(path: *const i8, out: *mut i8, out_size: usize) -> usize;
+            fn miri_host_to_target_path(
+                path: *const c_char,
+                out: *mut c_char,
+                out_size: usize,
+            ) -> usize;
         }
         let ret = miri_host_to_target_path(path.as_ptr(), out.as_mut_ptr(), out.capacity());
         assert_eq!(ret, 0);
diff --git a/src/tools/miri/tests/pass-dep/shims/libc-misc.rs b/src/tools/miri/tests/pass-dep/shims/libc-misc.rs
index 20e96a92c7c..98e1c3a0adb 100644
--- a/src/tools/miri/tests/pass-dep/shims/libc-misc.rs
+++ b/src/tools/miri/tests/pass-dep/shims/libc-misc.rs
@@ -7,7 +7,7 @@ use std::os::unix::io::AsRawFd;
 use std::path::PathBuf;
 
 fn tmp() -> PathBuf {
-    use std::ffi::{CStr, CString};
+    use std::ffi::{c_char, CStr, CString};
 
     let path = std::env::var("MIRI_TEMP")
         .unwrap_or_else(|_| std::env::temp_dir().into_os_string().into_string().unwrap());
@@ -17,7 +17,11 @@ fn tmp() -> PathBuf {
 
     unsafe {
         extern "Rust" {
-            fn miri_host_to_target_path(path: *const i8, out: *mut i8, out_size: usize) -> usize;
+            fn miri_host_to_target_path(
+                path: *const c_char,
+                out: *mut c_char,
+                out_size: usize,
+            ) -> usize;
         }
         let ret = miri_host_to_target_path(path.as_ptr(), out.as_mut_ptr(), out.capacity());
         assert_eq!(ret, 0);
diff --git a/src/tools/miri/tests/pass/shims/fs.rs b/src/tools/miri/tests/pass/shims/fs.rs
index a7d4800faec..7a9974f3938 100644
--- a/src/tools/miri/tests/pass/shims/fs.rs
+++ b/src/tools/miri/tests/pass/shims/fs.rs
@@ -6,7 +6,7 @@
 #![feature(is_terminal)]
 
 use std::collections::HashMap;
-use std::ffi::OsString;
+use std::ffi::{c_char, OsString};
 use std::fs::{
     canonicalize, create_dir, read_dir, read_link, remove_dir, remove_dir_all, remove_file, rename,
     File, OpenOptions,
@@ -39,7 +39,11 @@ fn host_to_target_path(path: String) -> PathBuf {
 
     unsafe {
         extern "Rust" {
-            fn miri_host_to_target_path(path: *const i8, out: *mut i8, out_size: usize) -> usize;
+            fn miri_host_to_target_path(
+                path: *const c_char,
+                out: *mut c_char,
+                out_size: usize,
+            ) -> usize;
         }
         let ret = miri_host_to_target_path(path.as_ptr(), out.as_mut_ptr(), out.capacity());
         assert_eq!(ret, 0);