diff --git a/crypto/md2/md2.h b/crypto/md2/md2.h
index 5b71855cb..a46120e7d 100644
--- a/crypto/md2/md2.h
+++ b/crypto/md2/md2.h
@@ -63,6 +63,7 @@
 #ifdef OPENSSL_NO_MD2
 #error MD2 is disabled.
 #endif
+#include <stddef.h>
 
 #define MD2_DIGEST_LENGTH	16
 #define MD2_BLOCK       	16
diff --git a/crypto/md4/md4.h b/crypto/md4/md4.h
index d289d287c..c3ed9b3f7 100644
--- a/crypto/md4/md4.h
+++ b/crypto/md4/md4.h
@@ -60,6 +60,7 @@
 #define HEADER_MD4_H
 
 #include <openssl/e_os2.h>
+#include <stddef.h>
 
 #ifdef  __cplusplus
 extern "C" {
diff --git a/crypto/md5/md5.h b/crypto/md5/md5.h
index d8c52345d..4cbf84386 100644
--- a/crypto/md5/md5.h
+++ b/crypto/md5/md5.h
@@ -60,6 +60,7 @@
 #define HEADER_MD5_H
 
 #include <openssl/e_os2.h>
+#include <stddef.h>
 
 #ifdef  __cplusplus
 extern "C" {
diff --git a/crypto/ripemd/ripemd.h b/crypto/ripemd/ripemd.h
index dea1f1821..5942eb618 100644
--- a/crypto/ripemd/ripemd.h
+++ b/crypto/ripemd/ripemd.h
@@ -60,6 +60,7 @@
 #define HEADER_RIPEMD_H
 
 #include <openssl/e_os2.h>
+#include <stddef.h>
 
 #ifdef  __cplusplus
 extern "C" {