diff --git a/configure.ac b/configure.ac
--- a/configure.ac
+++ b/configure.ac
@@ -46,6 +46,10 @@ AC_FUNC_MALLOC
 AC_TYPE_PID_T
 AC_TYPE_SIZE_T
 
+# to grab GNU-specific function prototypes for the following functions:
+# getline
+AC_DEFINE([_GNU_SOURCE], [1])
+
 #package dependencies:
 
 PKG_PROG_PKG_CONFIG(0.17.2)