diff --git a/configure.ac b/configure.ac
index cffefcf990f00a85ab619d573b21808149c588e6..eff477b3ade429d1239b58f1fb80791646bb4503 100644
--- a/configure.ac
+++ b/configure.ac
@@ -7,6 +7,11 @@ AC_CONFIG_SRCDIR([Makefile.am])
 AC_CONFIG_HEADERS([config.h])
 AC_CONFIG_MACRO_DIR([m4])
 
+# Set common system defines for POSIX extensions, such as _GNU_SOURCE
+# Must be called before any macros that run the compiler (like AC_PROG_LIBTOOL)
+# to avoid autoconf errors.
+AC_USE_SYSTEM_EXTENSIONS
+
 # Initialize Automake
 AM_INIT_AUTOMAKE([foreign dist-xz])