diff --git a/lib/autoconf/c.m4 b/lib/autoconf/c.m4
index ca63dc58..a31d2d33 100644
--- a/lib/autoconf/c.m4
+++ b/lib/autoconf/c.m4
@@ -1993,8 +1993,8 @@ AC_DEFUN([AC_C_FLEXIBLE_ARRAY_MEMBER],
 	    #include <stddef.h>
 	    struct s { int n; double d[]; };]],
 	  [[int m = getchar ();
-	    struct s *p = malloc (offsetof (struct s, d)
-				  + m * sizeof (double));
+	    struct s *p = (struct s *) malloc (offsetof (struct s, d)
+					       + m * sizeof (double));
 	    p->d[0] = 0.0;
 	    return p->d != (double *) NULL;]])],
        [ac_cv_c_flexmember=yes],
diff --git a/lib/autoconf/programs.m4 b/lib/autoconf/programs.m4
index b352ce24..63e07043 100644
--- a/lib/autoconf/programs.m4
+++ b/lib/autoconf/programs.m4
@@ -747,6 +747,9 @@ fi])])
 AC_DEFUN([_AC_PROG_LEX_YYTEXT_DECL],
 [cat >conftest.l <<_ACEOF[
 %{
+#ifdef __cplusplus
+extern "C"
+#endif
 int yywrap(void);
 %}
 %%