diff --git a/tools/bifcl/CMakeLists.txt b/tools/bifcl/CMakeLists.txt
index 114b78a74c..fb3dcac3af 100644
--- a/tools/bifcl/CMakeLists.txt
+++ b/tools/bifcl/CMakeLists.txt
@@ -16,6 +16,8 @@ if ( MISSING_PREREQS )
     message(FATAL_ERROR "Configuration aborted due to missing prerequisites")
 endif ()
 
+include(RequireCXX17)
+
 include_directories(BEFORE
                     ${CMAKE_CURRENT_SOURCE_DIR}/include
                     ${CMAKE_CURRENT_BINARY_DIR}
diff --git a/tools/bifcl/builtin-func.l b/tools/bifcl/builtin-func.l
index ad58f81f9e..9387bebd0d 100644
--- a/tools/bifcl/builtin-func.l
+++ b/tools/bifcl/builtin-func.l
@@ -2,6 +2,7 @@
 #include <ctype.h>
 #include <string.h>
 #include <unistd.h>
+#include <memory>
 #include "bif_arg.h"
 #include "bif_parse.h"
 
@@ -199,7 +200,8 @@ void init_alternative_mode()
 	fp_netvar_init = fp_func_init;
 
 	int n = 1024 + strlen(input_filename);
-	char auto_gen_comment[n];
+	auto auto_gen_comment_buf = std::make_unique<char[]>(n);
+	auto auto_gen_comment = auto_gen_comment_buf.get();
 
 	snprintf(auto_gen_comment, n,
 		 "This file was automatically generated by bifcl from %s (%s mode).",
@@ -365,7 +367,8 @@ int main(int argc, char* argv[])
 			fp_netvar_init = open_output_file("netvar_init");
 
 			int n = 1024 + strlen(input_filename);
-			char auto_gen_comment[n];
+			auto auto_gen_comment_buf = std::make_unique<char[]>(n);
+			auto auto_gen_comment = auto_gen_comment_buf.get();
 
 			snprintf(auto_gen_comment, n,
 				"This file was automatically generated by bifcl from %s.",