diff --git a/configure.ac b/configure.ac
index 261c45373a0d9ba7103bc06691796c3dae9534ce..18d5a28d6e59428e327dab3b97ad851b0e8a516c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -689,7 +689,7 @@ dnl debug mode is default-disabled
 AC_ARG_ENABLE([debug], AS_HELP_STRING([--enable-debug], [Build in debug mode, adds stricter warnings, disables optimization]))
 
 AS_IF([test "x$enable_debug" = "xyes"],
-      [CXXFLAGS="${CXXFLAGS} -g -fno-omit-frame-pointer -Wall -Wextra -Wnon-virtual-dtor -Wno-unknown-pragmas -O0"])
+      [CXXFLAGS="${CXXFLAGS} -g -fno-omit-frame-pointer -Wall -Wextra -Wnon-virtual-dtor -Wno-unknown-pragmas -Wformat=2 -O0"])
 
 dnl What Makefiles to generate