diff --git a/fips202.h b/fips202.h
index 871c209..d76083c 100644
--- a/fips202.h
+++ b/fips202.h
@@ -1,5 +1,5 @@
-#ifndef FIPS202_H
-#define FIPS202_H
+#ifndef XMSS_FIPS202_H
+#define XMSS_FIPS202_H
 
 #define SHAKE128_RATE 168
 #define SHAKE256_RATE 136
diff --git a/hash.h b/hash.h
index bbd2cf2..4bfe2d5 100644
--- a/hash.h
+++ b/hash.h
@@ -5,8 +5,8 @@ Joost Rijneveld
 Public domain.
 */
 
-#ifndef HASH_H
-#define HASH_H
+#ifndef XMSS_HASH_H
+#define XMSS_HASH_H
 
 #include "params.h"
 
diff --git a/hash_address.h b/hash_address.h
index 071d207..3944c79 100644
--- a/hash_address.h
+++ b/hash_address.h
@@ -5,6 +5,9 @@ Joost Rijneveld
 Public domain.
 */
 
+#ifndef XMSS_HASH_ADDRESS_H
+#define XMSS_HASH_ADDRESS_H
+
 #include <stdint.h>
 
 void set_layer_addr(uint32_t addr[8], uint32_t layer);
@@ -32,3 +35,5 @@ void set_ltree_addr(uint32_t addr[8], uint32_t ltree);
 void set_tree_height(uint32_t addr[8], uint32_t treeHeight);
 
 void set_tree_index(uint32_t addr[8], uint32_t treeIndex);
+
+#endif
diff --git a/params.h b/params.h
index c15a80d..bafa79e 100644
--- a/params.h
+++ b/params.h
@@ -1,5 +1,5 @@
-#ifndef PARAMS_H
-#define PARAMS_H
+#ifndef XMSS_PARAMS_H
+#define XMSS_PARAMS_H
 
 #include <stdint.h>
 
diff --git a/randombytes.h b/randombytes.h
index 053d3f1..65cf221 100644
--- a/randombytes.h
+++ b/randombytes.h
@@ -1,5 +1,5 @@
-#ifndef RANDOMBYTES_H
-#define RANDOMBYTES_H
+#ifndef XMSS_RANDOMBYTES_H
+#define XMSS_RANDOMBYTES_H
 
 extern void randombytes(unsigned char * x,unsigned long long xlen);
 
diff --git a/wots.h b/wots.h
index 0aeb98f..c67b27c 100644
--- a/wots.h
+++ b/wots.h
@@ -5,8 +5,8 @@ Joost Rijneveld
 Public domain.
 */
 
-#ifndef WOTS_H
-#define WOTS_H
+#ifndef XMSS_WOTS_H
+#define XMSS_WOTS_H
 
 #include <stdint.h>
 #include "params.h"