diff --git a/tests/data/Makefile.am b/tests/data/Makefile.am
index 18cf6c0365..a72f6740f8 100644
--- a/tests/data/Makefile.am
+++ b/tests/data/Makefile.am
@@ -278,7 +278,7 @@ test3032 \
 test3100 test3101 test3102 test3103 test3104 test3105 \
 \
 test3200 test3201 test3202 test3203 test3204 test3205 test3207 test3208 \
-test3209 test3210 test3211 test3212 test3213 \
+test3209 test3210 test3211 test3212 test3213 test3214 \
 \
 test4000 test4001
 
diff --git a/tests/data/test3214 b/tests/data/test3214
new file mode 100644
index 0000000000..626548e515
--- /dev/null
+++ b/tests/data/test3214
@@ -0,0 +1,22 @@
+<testcase>
+<info>
+<keywords>
+unittest
+size
+</keywords>
+</info>
+
+#
+# Client-side
+<client>
+<server>
+none
+</server>
+<features>
+unittest
+</features>
+<name>
+struct size checks
+</name>
+</client>
+</testcase>
diff --git a/tests/unit/Makefile.inc b/tests/unit/Makefile.inc
index e01980e9cc..17d257fb55 100644
--- a/tests/unit/Makefile.inc
+++ b/tests/unit/Makefile.inc
@@ -45,4 +45,4 @@ TESTS_C = \
   unit1979.c unit1980.c \
   unit2600.c unit2601.c unit2602.c unit2603.c unit2604.c \
   unit3200.c                                             unit3205.c \
-  unit3211.c unit3212.c unit3213.c
+  unit3211.c unit3212.c unit3213.c unit3214.c
diff --git a/tests/unit/unit3214.c b/tests/unit/unit3214.c
new file mode 100644
index 0000000000..f1f88c078a
--- /dev/null
+++ b/tests/unit/unit3214.c
@@ -0,0 +1,85 @@
+/***************************************************************************
+ *                                  _   _ ____  _
+ *  Project                     ___| | | |  _ \| |
+ *                             / __| | | | |_) | |
+ *                            | (__| |_| |  _ <| |___
+ *                             \___|\___/|_| \_\_____|
+ *
+ * Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
+ *
+ * This software is licensed as described in the file COPYING, which
+ * you should have received as part of this distribution. The terms
+ * are also available at https://curl.se/docs/copyright.html.
+ *
+ * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+ * copies of the Software, and permit persons to whom the Software is
+ * furnished to do so, under the terms of the COPYING file.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ * SPDX-License-Identifier: curl
+ *
+ ***************************************************************************/
+#include "curlcheck.h"
+
+#include "urldata.h"
+
+static void checksize(const char *name, size_t size, size_t allowed)
+{
+  if(size > allowed) {
+    fprintf(stderr, "BAD: struct %s is %d bytes, allowed to be %d",
+            name, (int)size, (int)allowed);
+    fprintf(stderr, ": %d bytes too big\n", (int)(size - allowed));
+    unitfail++;
+  }
+  else {
+    printf("FINE: struct %s is %d bytes, allowed %d (margin: %d bytes)\n",
+           name, (int)size, (int)allowed, (int)(allowed - size));
+  }
+}
+
+/* the maximum sizes we allow specific structs to grow to */
+#define MAX_CURL_EASY           5800
+#define MAX_CONNECTDATA         1300
+#define MAX_CURL_MULTI          750
+#define MAX_CURL_HTTPPOST       112
+#define MAX_CURL_SLIST          16
+#define MAX_CURL_KHKEY          24
+#define MAX_CURL_HSTSENTRY      40
+#define MAX_CURL_INDEX          16
+#define MAX_CURL_MIME           96
+#define MAX_CURL_MIMEPART       440
+#define MAX_CURL_CERTINFO       16
+#define MAX_CURL_TLSSESSIONINFO 16
+#define MAX_CURL_BLOB           24
+#define MAX_CURLMSG             24
+#define MAX_CURL_HEADER         48
+
+static CURLcode test_unit3214(char *arg)
+{
+  UNITTEST_BEGIN_SIMPLE
+
+  checksize("Curl_easy", sizeof(struct Curl_easy), MAX_CURL_EASY);
+  checksize("connectdata", sizeof(struct connectdata), MAX_CONNECTDATA);
+  checksize("Curl_multi", sizeof(struct Curl_multi), MAX_CURL_MULTI);
+
+  /* public structs MUST NOT change (unless controlled), but exact sizes
+     depend on architecure */
+  checksize("curl_httppost", sizeof(struct curl_httppost), MAX_CURL_HTTPPOST);
+  checksize("curl_slist", sizeof(struct curl_slist), MAX_CURL_SLIST);
+  checksize("curl_khkey", sizeof(struct curl_khkey), MAX_CURL_KHKEY);
+  checksize("curl_hstsentry", sizeof(struct curl_hstsentry),
+            MAX_CURL_HSTSENTRY);
+  checksize("curl_index", sizeof(struct curl_index), MAX_CURL_INDEX);
+  checksize("curl_mime", sizeof(struct curl_mime), MAX_CURL_MIME);
+  checksize("curl_mimepart", sizeof(struct curl_mimepart), MAX_CURL_MIMEPART);
+  checksize("curl_certinfo", sizeof(struct curl_certinfo), MAX_CURL_CERTINFO);
+  checksize("curl_tlssessioninfo", sizeof(struct curl_tlssessioninfo),
+            MAX_CURL_TLSSESSIONINFO);
+  checksize("curl_blob", sizeof(struct curl_blob), MAX_CURL_BLOB);
+  checksize("CURLMsg", sizeof(struct CURLMsg), MAX_CURLMSG);
+  checksize("curl_header", sizeof(struct curl_header), MAX_CURL_HEADER);
+
+  UNITTEST_END_SIMPLE
+}