diff --git a/src/os_unix.h b/src/os_unix.h
index 618c0e9..a7a0c84 100644
--- a/src/os_unix.h
+++ b/src/os_unix.h
@@ -127,9 +127,16 @@
 # endif
 #endif
 
+// on some systems time.h should not be included together with sys/time.h
 #if !defined(HAVE_SYS_TIME_H) || defined(TIME_WITH_SYS_TIME)
-# include <time.h>	    /* on some systems time.h should not be
-			       included together with sys/time.h */
+// Needed for strptime()
+# ifndef _XOPEN_SOURCE
+#  define _XOPEN_SOURCE
+# endif
+# ifndef __USE_XOPEN
+#  define __USE_XOPEN
+# endif
+# include <time.h>
 #endif
 #ifdef HAVE_SYS_TIME_H
 # include <sys/time.h>