diff --git a/libs/freetdm/configure.ac b/libs/freetdm/configure.ac
index 3ff905cf26..6234a100e9 100644
--- a/libs/freetdm/configure.ac
+++ b/libs/freetdm/configure.ac
@@ -32,7 +32,7 @@ AX_COMPILER_VENDOR
 
 case "${ax_cv_c_compiler_vendor}" in
 gnu)
-    COMP_VENDOR_CFLAGS="-std=gnu99 -ffast-math -Wall -Werror -Wunused-variable -Wwrite-strings -Wstrict-prototypes -Wmissing-prototypes"
+    COMP_VENDOR_CFLAGS="-ffast-math -Wall -Werror -Wunused-variable -Wwrite-strings -Wstrict-prototypes -Wmissing-prototypes"
     ;;
 sun)
     COMP_VENDOR_CFLAGS="-xc99=all -mt -xCC -D__FUNCTION__=__func__ -xvpara"