diff --git a/missing/crypt.h b/missing/crypt.h
index 7a78767931..7c2642f593 100644
--- a/missing/crypt.h
+++ b/missing/crypt.h
@@ -237,8 +237,6 @@ struct crypt_data {
 	char	cryptresult[1+4+4+11+1];	/* encrypted result */
 };
 
-#define SIZEOF_CRYPT_DATA (KS_SIZE*8+(1+4+4+11+1))
-
 char *crypt(const char *key, const char *setting);
 void setkey(const char *key);
 void encrypt(char *block, int flag);
diff --git a/string.c b/string.c
index 5731807379..983fa919fa 100644
--- a/string.c
+++ b/string.c
@@ -8839,14 +8839,9 @@ rb_str_oct(VALUE str)
 static VALUE
 rb_str_crypt(VALUE str, VALUE salt)
 {
-#undef LARGE_CRYPT_DATA
 #ifdef HAVE_CRYPT_R
-# if defined SIZEOF_CRYPT_DATA && SIZEOF_CRYPT_DATA <= 256
-    struct crypt_data cdata, *const data = &cdata;
-# else
-#   define LARGE_CRYPT_DATA
-    struct crypt_data *data = ALLOC(struct crypt_data);
-# endif
+    VALUE databuf;
+    struct crypt_data *data;
 #else
     extern char *crypt(const char *, const char *);
 #endif
@@ -8877,6 +8872,7 @@ rb_str_crypt(VALUE str, VALUE salt)
     }
 #endif
 #ifdef HAVE_CRYPT_R
+    data = ALLOCV(databuf, sizeof(struct crypt_data));
 # ifdef HAVE_STRUCT_CRYPT_DATA_INITIALIZED
     data->initialized = 0;
 # endif
@@ -8885,17 +8881,15 @@ rb_str_crypt(VALUE str, VALUE salt)
     res = crypt(s, saltp);
 #endif
     if (!res) {
-#ifdef LARGE_CRYPT_DATA
+#ifdef HAVE_CRYPT_R
 	int err = errno;
-	xfree(data);
+	ALLOCV_END(databuf);
 	errno = err;
 #endif
 	rb_sys_fail("crypt");
     }
     result = rb_str_new_cstr(res);
-#ifdef LARGE_CRYPT_DATA
-    xfree(data);
-#endif
+    ALLOCV_END(databuf);
     FL_SET_RAW(result, OBJ_TAINTED_RAW(str) | OBJ_TAINTED_RAW(salt));
     return result;
 }