diff --git a/include/pcp.h b/include/pcp.h
index b9881a9..0d7b910 100644
--- a/include/pcp.h
+++ b/include/pcp.h
@@ -5,6 +5,22 @@
 extern "C" {
 #endif
 
+#if defined __linux__ || defined __GNU__ || defined __GLIBC__
+#  ifndef _DEFAULT_SOURCE
+#    define _DEFAULT_SOURCE 1
+#  endif
+#
+#  ifndef _XOPEN_SOURCE
+#    define _XOPEN_SOURCE 1
+#  endif
+#
+#  ifndef _GNU_SOURCE
+#    define _GNU_SOURCE 1
+#  endif
+#else
+#  define _BSD_SOURCE 1
+#endif
+
 #include "pcp/config.h"
 #include "pcp/base85.h"
 #include "pcp/buffer.h"
diff --git a/include/pcp/mgmt.h b/include/pcp/mgmt.h
index ebd069b..21b2978 100644
--- a/include/pcp/mgmt.h
+++ b/include/pcp/mgmt.h
@@ -26,6 +26,22 @@
 #ifndef _HAVE_PCP_MGMT_H
 #define _HAVE_PCP_MGMT_H
 
+#if defined __linux__ || defined __GNU__ || defined __GLIBC__
+#  ifndef _DEFAULT_SOURCE
+#    define _DEFAULT_SOURCE 1
+#  endif
+#
+#  ifndef _XOPEN_SOURCE
+#    define _XOPEN_SOURCE 1
+#  endif
+#
+#  ifndef _GNU_SOURCE
+#    define _GNU_SOURCE 1
+#  endif
+#else
+#  define _BSD_SOURCE 1
+#endif
+
 #include <sodium.h>
 #include <string.h>
 #include <stdio.h>
diff --git a/src/pcp.h b/src/pcp.h
index 5344671..e5bb9f8 100644
--- a/src/pcp.h
+++ b/src/pcp.h
@@ -23,12 +23,6 @@
 #ifndef _HAVE_PCP_H
 #define _HAVE_PCP_H
 
-#if defined __linux__ || defined __GNU__ || defined __GLIBC__
-#define _DEFAULT_SOURCE 1
-#else
-#define _BSD_SOURCE 1
-#endif
-
 #include <unistd.h>
 #include <stdio.h>
 #include <stdlib.h>