diff --git a/mfapi/file.c b/mfapi/file.c
index 3428997..2b6512b 100644
--- a/mfapi/file.c
+++ b/mfapi/file.c
@@ -18,6 +18,7 @@
  */
 
 #define _POSIX_C_SOURCE 200809L // for strdup
+#define _BSD_SOURCE             // for strdup on old systems
 
 #include <stdint.h>
 #include <stdio.h>
diff --git a/mfapi/mfconn.c b/mfapi/mfconn.c
index 8a9a0e3..7e18642 100644
--- a/mfapi/mfconn.c
+++ b/mfapi/mfconn.c
@@ -18,6 +18,7 @@
  */
 
 #define _POSIX_C_SOURCE 200809L // for strdup
+#define _BSD_SOURCE             // for strdup on old systems
 
 #include <openssl/md5.h>
 #include <openssl/sha.h>
diff --git a/mfapi/patch.c b/mfapi/patch.c
index 76bcb1c..a96dcf4 100644
--- a/mfapi/patch.c
+++ b/mfapi/patch.c
@@ -17,6 +17,7 @@
  */
 
 #define _POSIX_C_SOURCE 200809L // for strdup
+#defein _BSD_SOURCE             // for strdup on old systems
 
 #include <stdint.h>
 #include <openssl/sha.h>