diff --git a/engines/e_4758_cca.c b/engines/e_4758_cca.c
index 2e77f8c647..203a8a75e6 100644
--- a/engines/e_4758_cca.c
+++ b/engines/e_4758_cca.c
@@ -54,6 +54,7 @@
  */
 
 #include <stdio.h>
+#include <string.h>
 #include <openssl/crypto.h>
 /* #include <openssl/pem.h> */
 #include <openssl/dso.h>
diff --git a/engines/e_atalla.c b/engines/e_atalla.c
index be590f0ebb..65339a0d68 100644
--- a/engines/e_atalla.c
+++ b/engines/e_atalla.c
@@ -57,6 +57,7 @@
  */
 
 #include <stdio.h>
+#include <string.h>
 #include <openssl/crypto.h>
 #include <openssl/buffer.h>
 #include <openssl/dso.h>
diff --git a/engines/e_cswift.c b/engines/e_cswift.c
index 2ed9357f13..f3d3628366 100644
--- a/engines/e_cswift.c
+++ b/engines/e_cswift.c
@@ -57,6 +57,7 @@
  */
 
 #include <stdio.h>
+#include <string.h>
 #include <openssl/crypto.h>
 #include <openssl/buffer.h>
 #include <openssl/dso.h>
diff --git a/engines/e_sureware.c b/engines/e_sureware.c
index dced97c695..9c2279c195 100644
--- a/engines/e_sureware.c
+++ b/engines/e_sureware.c
@@ -51,6 +51,7 @@
 ====================================================================*/
 
 #include <stdio.h>
+#include <string.h>
 #include <openssl/crypto.h>
 #include <openssl/pem.h>
 #include <openssl/dso.h>
diff --git a/engines/e_ubsec.c b/engines/e_ubsec.c
index fe4a3b7ef7..35af495b71 100644
--- a/engines/e_ubsec.c
+++ b/engines/e_ubsec.c
@@ -59,6 +59,7 @@
  */
 
 #include <stdio.h>
+#include <string.h>
 #include <openssl/crypto.h>
 #include <openssl/buffer.h>
 #include <openssl/dso.h>