diff --git a/src/platform.h b/src/platform.h
index fba2078bb..662d51e40 100644
--- a/src/platform.h
+++ b/src/platform.h
@@ -21,6 +21,7 @@
 #pragma warning(disable: 4457) // declaration hides function parameter
 #pragma warning(disable: 4459) // declaration hides global
 #else /* assume gcc */
+#define __USE_BSD
 #if !defined(__STDC_VERSION__) || __STDC_VERSION__ < 199901L
 # define va_copy(a,b) __va_copy(a,b)
 #endif