diff --git a/src/main.c b/src/main.c
index 88824c3..45c1e03 100644
--- a/src/main.c
+++ b/src/main.c
@@ -24,6 +24,10 @@
 #define O_CLOEXEC 0
 #endif
 
+#ifndef PACKAGE_STRING
+#define PACKAGE_STRING "unknown"
+#endif
+
 #define GT_MTU(X) ((X)-28)
 
 static struct {