diff --git a/plugins/sudoers/b64_decode.c b/plugins/sudoers/b64_decode.c
index 6242888730..c7dd73e21a 100644
--- a/plugins/sudoers/b64_decode.c
+++ b/plugins/sudoers/b64_decode.c
@@ -54,7 +54,7 @@ static const unsigned char base64dec_tab[256]= {
  * result in dst.
  */
 size_t
-base64_decode(const char *in, unsigned char *out, size_t out_size)
+base64_decode(const char * restrict in, unsigned char * restrict out, size_t out_size)
 {
     unsigned char *out_end = out + out_size;
     const unsigned char *out0 = out;
diff --git a/plugins/sudoers/b64_encode.c b/plugins/sudoers/b64_encode.c
index 1e1afa0db7..bf5e7be5d5 100644
--- a/plugins/sudoers/b64_encode.c
+++ b/plugins/sudoers/b64_encode.c
@@ -29,7 +29,7 @@ static const unsigned char base64enc_tab[64] =
     "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
 
 size_t
-base64_encode(const unsigned char *in, size_t in_len, char *out, size_t out_len)
+base64_encode(const unsigned char * restrict in, size_t in_len, char * restrict out, size_t out_len)
 {
     size_t ii, io;
     unsigned int rem, v;
diff --git a/plugins/sudoers/parse.h b/plugins/sudoers/parse.h
index 2c6d8660ad..f63e1d7395 100644
--- a/plugins/sudoers/parse.h
+++ b/plugins/sudoers/parse.h
@@ -446,8 +446,8 @@ extern FILE *sudoersin;
 extern char *sudoers;
 
 /* base64.c */
-size_t base64_decode(const char *str, unsigned char *dst, size_t dsize);
-size_t base64_encode(const unsigned char *in, size_t in_len, char *out, size_t out_len);
+size_t base64_decode(const char * restrict str, unsigned char *dst, size_t dsize);
+size_t base64_encode(const unsigned char * restrict in, size_t in_len, char * restrict out, size_t out_len);
 
 /* timeout.c */
 int parse_timeout(const char *timestr);