diff --git a/plugins/sudoers/prompt.c b/plugins/sudoers/prompt.c
index 0bf9f7928..50e93896e 100644
--- a/plugins/sudoers/prompt.c
+++ b/plugins/sudoers/prompt.c
@@ -40,8 +40,8 @@
  * the dynamically allocated result.
  */
 char *
-expand_prompt(const struct sudoers_context *ctx, const char *old_prompt,
-    const char *auth_user)
+expand_prompt(const struct sudoers_context *ctx,
+        const char *restrict old_prompt, const char *restrict auth_user)
 {
     size_t len, n;
     int subst;
diff --git a/plugins/sudoers/strlcpy_unesc.c b/plugins/sudoers/strlcpy_unesc.c
index 56a7a4eb7..3df6e8b6c 100644
--- a/plugins/sudoers/strlcpy_unesc.c
+++ b/plugins/sudoers/strlcpy_unesc.c
@@ -33,7 +33,7 @@
  * Like strlcpy() but collapses non-space chars escaped with a backslash.
  */
 size_t
-strlcpy_unescape(char *dst, const char *src, size_t size)
+strlcpy_unescape(char *restrict dst, const char *restrict src, size_t size)
 {
     size_t len = 0;
     char ch;
diff --git a/plugins/sudoers/sudoers.h b/plugins/sudoers/sudoers.h
index 46f1cc4fe..ec34b22e1 100644
--- a/plugins/sudoers/sudoers.h
+++ b/plugins/sudoers/sudoers.h
@@ -333,7 +333,7 @@ int check_user_runchroot(const char *runchroot);
 int check_user_runcwd(const char *runcwd);
 
 /* prompt.c */
-char *expand_prompt(const struct sudoers_context *ctx, const char *old_prompt, const char *auth_user);
+char *expand_prompt(const struct sudoers_context *ctx, const char *restrict old_prompt, const char *restrict auth_user);
 
 /* sudo_auth.c */
 bool sudo_auth_needs_end_session(void);
@@ -494,7 +494,7 @@ void canon_path_free(char *resolved);
 void canon_path_free_cache(void);
 
 /* strlcpy_unesc.c */
-size_t strlcpy_unescape(char *dst, const char *src, size_t size);
+size_t strlcpy_unescape(char *restrict dst, const char *restrict src, size_t size);
 
 /* strvec_join.c */
 char *strvec_join(char *const argv[], char sep, size_t (*cpy)(char *, const char *, size_t));