diff --git a/tools/bifcl/builtin-func.l b/tools/bifcl/builtin-func.l
index 5b98f054d4..8f0468ceab 100644
--- a/tools/bifcl/builtin-func.l
+++ b/tools/bifcl/builtin-func.l
@@ -23,7 +23,7 @@ char* copy_string(const char* s)
 
 int line_number = 1;
 
-extern int in_c_code;
+extern bool in_c_code;
 
 int check_c_mode(int t)
 	{
@@ -156,7 +156,7 @@ extern int yyparse();
 char* input_filename = nullptr;
 char* input_filename_with_path = nullptr;
 char* plugin = nullptr;
-int   alternative_mode = 0;
+bool  alternative_mode = false;
 
 FILE* fp_zeek_init = nullptr;
 FILE* fp_func_def = nullptr;
@@ -339,12 +339,12 @@ int main(int argc, char* argv[])
 		{
 		switch ( opt ) {
 		case 'p':
-			alternative_mode = 1;
+			alternative_mode = true;
 			plugin = (char*) optarg;
 			break;
 
 		case 's':
-			alternative_mode = 1;
+			alternative_mode = true;
 			break;
 
 		default:
diff --git a/tools/bifcl/builtin-func.y b/tools/bifcl/builtin-func.y
index 2188eb3293..365ff15bd3 100644
--- a/tools/bifcl/builtin-func.y
+++ b/tools/bifcl/builtin-func.y
@@ -17,7 +17,7 @@ extern int line_number;
 extern char* input_filename;
 extern char* input_filename_with_path;
 extern char* plugin;
-extern int alternative_mode;
+extern bool alternative_mode;
 
 #define print_line_directive(fp) fprintf(fp, "\n#line %d \"%s\"\n", line_number, input_filename_with_path)
 
@@ -29,7 +29,7 @@ extern FILE* fp_netvar_h;
 extern FILE* fp_netvar_def;
 extern FILE* fp_netvar_init;
 
-int in_c_code = 0;
+bool in_c_code = false;
 string current_module = GLOBAL_MODULE_NAME;
 int definition_type;
 string type_name;
@@ -686,13 +686,13 @@ body:		body_start c_body body_end
 
 c_code_begin:	/* empty */
 			{
-			in_c_code = 1;
+			in_c_code = true;
 			print_line_directive(fp_func_def);
 			}
 	;
 
 c_code_end:	/* empty */
-			{ in_c_code = 0; }
+			{ in_c_code = false; }
 	;
 
 body_start:	TOK_LPB c_code_begin