diff --git a/md5sum.c b/md5sum.c
index 0de1cb6..4db3063 100644
--- a/md5sum.c
+++ b/md5sum.c
@@ -7,7 +7,7 @@
 #include "md5.h"
 #include "util.h"
 
-struct md5 s;
+static struct md5 s;
 struct crypt_ops md5_ops = {
 	md5_init,
 	md5_update,
diff --git a/sha1sum.c b/sha1sum.c
index 3438c7f..3865581 100644
--- a/sha1sum.c
+++ b/sha1sum.c
@@ -7,7 +7,7 @@
 #include "sha1.h"
 #include "util.h"
 
-struct sha1 s;
+static struct sha1 s;
 struct crypt_ops sha1_ops = {
 	sha1_init,
 	sha1_update,
diff --git a/sha256sum.c b/sha256sum.c
index aa642a4..908dc26 100644
--- a/sha256sum.c
+++ b/sha256sum.c
@@ -7,7 +7,7 @@
 #include "sha256.h"
 #include "util.h"
 
-struct sha256 s;
+static struct sha256 s;
 struct crypt_ops sha256_ops = {
 	sha256_init,
 	sha256_update,
diff --git a/sha512sum.c b/sha512sum.c
index ca835e8..a467f12 100644
--- a/sha512sum.c
+++ b/sha512sum.c
@@ -7,7 +7,7 @@
 #include "sha512.h"
 #include "util.h"
 
-struct sha512 s;
+static struct sha512 s;
 struct crypt_ops sha512_ops = {
 	sha512_init,
 	sha512_update,