diff --git a/editcap.c b/editcap.c
index 4084652418..2a11bf7a10 100644
--- a/editcap.c
+++ b/editcap.c
@@ -18,10 +18,14 @@
 
 /*
  * Just make sure we include the prototype for strptime as well
- * (needed for glibc 2.2)
+ * (needed for glibc 2.2) but make sure we do this only if not
+ * yet defined.
  */
 
-#define __USE_XOPEN
+#ifndef __USE_XOPEN
+#  define __USE_XOPEN
+#endif
+
 #include <time.h>
 #include <glib.h>
 
diff --git a/epan/ftypes/ftype-time.c b/epan/ftypes/ftype-time.c
index cd2663ac80..ed50e3b160 100644
--- a/epan/ftypes/ftype-time.c
+++ b/epan/ftypes/ftype-time.c
@@ -29,9 +29,12 @@
 
 /*
  * Just make sure we include the prototype for strptime as well
- * (needed for glibc 2.2)
+ * (needed for glibc 2.2) but make sure we do this only if not
+ * yet defined.
  */
-#define __USE_XOPEN
+#ifndef __USE_XOPEN
+#  define __USE_XOPEN
+#endif
 
 #include <time.h>
 
diff --git a/text2pcap.c b/text2pcap.c
index ea058f2249..a7349b9ce5 100644
--- a/text2pcap.c
+++ b/text2pcap.c
@@ -88,9 +88,12 @@
 
 /*
  * Just make sure we include the prototype for strptime as well
- * (needed for glibc 2.2)
+ * (needed for glibc 2.2) but make sure we do this only if not
+ * yet defined.
  */
-#define __USE_XOPEN
+#ifndef
+#  define __USE_XOPEN
+#endif
 
 #include <time.h>
 #include <glib.h>