diff --git a/library/sha512.c b/library/sha512.c
index 629ed1b..4074d33 100644
--- a/library/sha512.c
+++ b/library/sha512.c
@@ -488,7 +488,7 @@
 /*
  * FIPS-180-2 test vectors
  */
-static unsigned char sha512_test_buf[3][113] =
+static const unsigned char sha512_test_buf[3][113] =
 {
     { "abc" },
     { "abcdefghbcdefghicdefghijdefghijkefghijklfghijklmghijklmn"
@@ -557,7 +557,7 @@
 /*
  * RFC 4231 test vectors
  */
-static unsigned char sha512_hmac_test_key[7][26] =
+static const unsigned char sha512_hmac_test_key[7][26] =
 {
     { "\x0B\x0B\x0B\x0B\x0B\x0B\x0B\x0B\x0B\x0B\x0B\x0B\x0B\x0B\x0B\x0B"
       "\x0B\x0B\x0B\x0B" },
@@ -577,7 +577,7 @@
     20, 4, 20, 25, 20, 131, 131
 };
 
-static unsigned char sha512_hmac_test_buf[7][153] =
+static const unsigned char sha512_hmac_test_buf[7][153] =
 {
     { "Hi There" },
     { "what do ya want for nothing?" },