diff --git a/client/whereami.c b/client/whereami.c
index 021ad874..7c09894f 100644
--- a/client/whereami.c
+++ b/client/whereami.c
@@ -10,6 +10,11 @@
 extern "C" {
 #endif
 
+#if defined(__linux__)
+// make realpath() available:
+#define _DEFAULT_SOURCE
+#endif
+
 #if !defined(WAI_MALLOC) || !defined(WAI_FREE) || !defined(WAI_REALLOC)
 #include <stdlib.h>
 #endif