diff --git a/Orange/classification/_simple_tree.c b/Orange/classification/_simple_tree.c
index 448c625dd2b..fe91cd2a283 100644
--- a/Orange/classification/_simple_tree.c
+++ b/Orange/classification/_simple_tree.c
@@ -1,3 +1,6 @@
+#if (defined __GLIBC__ || defined __GNU__ || defined __linux__)
+#define _GNU_SOURCE
+#endif
 #include <math.h>
 #include <float.h>
 #include <assert.h>