diff --git a/library/md5.c b/library/md5.c
index 9c5d73aae..b68bd4bc9 100644
--- a/library/md5.c
+++ b/library/md5.c
@@ -580,7 +580,7 @@ int md5_self_test( int verbose )
 
         if( i == 5 || i == 6 )
         {
-            memset( buf, '\xAA', buflen = 80 );
+            memset( buf, 0xAA, buflen = 80 );
             md5_hmac_starts( &ctx, buf, buflen );
         }
         else
diff --git a/library/sha1.c b/library/sha1.c
index c477e9a61..604f8ee16 100644
--- a/library/sha1.c
+++ b/library/sha1.c
@@ -622,7 +622,7 @@ int sha1_self_test( int verbose )
 
         if( i == 5 || i == 6 )
         {
-            memset( buf, '\xAA', buflen = 80 );
+            memset( buf, 0xAA, buflen = 80 );
             sha1_hmac_starts( &ctx, buf, buflen );
         }
         else
diff --git a/library/sha256.c b/library/sha256.c
index dedc6b84f..39444bc89 100644
--- a/library/sha256.c
+++ b/library/sha256.c
@@ -703,7 +703,7 @@ int sha256_self_test( int verbose )
 
         if( j == 5 || j == 6 )
         {
-            memset( buf, '\xAA', buflen = 131 );
+            memset( buf, 0xAA, buflen = 131 );
             sha256_hmac_starts( &ctx, buf, buflen, k );
         }
         else
diff --git a/library/sha512.c b/library/sha512.c
index ed044ed80..5decc8fac 100644
--- a/library/sha512.c
+++ b/library/sha512.c
@@ -757,7 +757,7 @@ int sha512_self_test( int verbose )
 
         if( j == 5 || j == 6 )
         {
-            memset( buf, '\xAA', buflen = 131 );
+            memset( buf, 0xAA, buflen = 131 );
             sha512_hmac_starts( &ctx, buf, buflen, k );
         }
         else