diff --git a/fractal.c b/fractal.c
index 722788e..40ee0fd 100644
--- a/fractal.c
+++ b/fractal.c
@@ -10,6 +10,11 @@
  * Dedication along with this software. If not, see
  * <http://creativecommons.org/publicdomain/zero/1.0/>.
  */
+/* gepopt visibility for GLIBC */
+#if !defined(__OpenBSD__)
+#define _DEFAULT_SOURCE
+#endif
+
 #include <errno.h>
 #include <inttypes.h>
 #include <limits.h>
diff --git a/fun-gen.c b/fun-gen.c
index cce32d0..a86c562 100644
--- a/fun-gen.c
+++ b/fun-gen.c
@@ -10,6 +10,11 @@
  * Dedication along with this software. If not, see
  * <http://creativecommons.org/publicdomain/zero/1.0/>.
  */
+/* gepopt visibility for GLIBC */
+#if !defined(__OpenBSD__)
+#define _DEFAULT_SOURCE
+#endif
+
 #include <errno.h>
 #include <inttypes.h>
 #include <limits.h>
diff --git a/julia.c b/julia.c
index 2fe7d32..bdecdfa 100644
--- a/julia.c
+++ b/julia.c
@@ -10,6 +10,11 @@
  * Dedication along with this software. If not, see
  * <http://creativecommons.org/publicdomain/zero/1.0/>.
  */
+/* gepopt visibility for GLIBC */
+#if !defined(__OpenBSD__)
+#define _DEFAULT_SOURCE
+#endif
+
 #include <complex.h>
 #include <errno.h>
 #include <inttypes.h>
diff --git a/palette.c b/palette.c
index a8a6b46..f2ced23 100644
--- a/palette.c
+++ b/palette.c
@@ -10,6 +10,11 @@
  * Dedication along with this software. If not, see
  * <http://creativecommons.org/publicdomain/zero/1.0/>.
  */
+/* gepopt visibility for GLIBC */
+#if !defined(__OpenBSD__)
+#define _DEFAULT_SOURCE
+#endif
+
 #include <errno.h>
 #include <inttypes.h>
 #include <limits.h>