diff --git a/lib/multi.c b/lib/multi.c
index 792b30515d..b744e03ae5 100644
--- a/lib/multi.c
+++ b/lib/multi.c
@@ -347,7 +347,8 @@ static CURLMcode multi_xfers_add(struct Curl_multi *multi,
   if(unused <= min_unused) {
      /* make it a 64 multiple, since our bitsets frow by that and
       * small (easy_multi) grows to at least 64 on first resize. */
-    unsigned int newsize = ((capacity + min_unused) + 63) / 64;
+    unsigned int newsize = (((capacity + min_unused) + 63) / 64) * 64;
+    DEBUGASSERT(newsize > capacity);
     /* Grow the bitsets first. Should one fail, we do not need
      * to downsize the already resized ones. The sets continue
      * to work properly when larger than the table, but not
diff --git a/tests/data/Makefile.am b/tests/data/Makefile.am
index e8f9e12be7..16bb57db8e 100644
--- a/tests/data/Makefile.am
+++ b/tests/data/Makefile.am
@@ -107,7 +107,7 @@ test709 test710 test711 test712 test713 test714 test715 test716 test717 \
 test718 test719 test720 test721 test722 test723 test724 test725 test726 \
 test727 test728 test729 test730 test731 test732 test733 test734 test735 \
 test736 test737 test738 test739 test740 test741 test742 test743 test744 \
-test745 test746 test747 test748 test749 test750 \
+test745 test746 test747 test748 test749 test750 test751 \
 \
 test780 test781 test782 test783 test784 test785 test786 test787 test788 \
 test789 test790 test791 \
diff --git a/tests/data/test751 b/tests/data/test751
new file mode 100644
index 0000000000..ffc6df512f
--- /dev/null
+++ b/tests/data/test751
@@ -0,0 +1,33 @@
+<testcase>
+<info>
+<keywords>
+MULTI
+</keywords>
+</info>
+<reply>
+<data>
+</data>
+</reply>
+
+# Client-side
+<client>
+<server>
+none
+</server>
+# tool is what to use instead of 'curl'
+<tool>
+lib%TESTNUMBER
+</tool>
+
+<name>
+multi - add many easy handles
+</name>
+<command>
+</command>
+</file>
+</client>
+
+# Verify data after the test has been "shot"
+<verify>
+</verify>
+</testcase>
diff --git a/tests/libtest/Makefile.inc b/tests/libtest/Makefile.inc
index faf7eacdf6..002e7ab547 100644
--- a/tests/libtest/Makefile.inc
+++ b/tests/libtest/Makefile.inc
@@ -50,6 +50,7 @@ LIBTESTPROGS = libauthretry libntlmconnect libprereq                     \
  lib659 lib661 lib666 lib667 lib668 \
  lib670 lib671 lib672 lib673 lib674 lib676 lib677 lib678 lib694 lib695   \
  lib696 \
+ lib751 \
  lib1156 \
  lib1301 \
  lib1308 \
@@ -349,6 +350,9 @@ lib695_SOURCES = lib695.c $(SUPPORTFILES)
 lib696_SOURCES = lib556.c $(SUPPORTFILES) $(WARNLESS)
 lib696_CPPFLAGS = $(AM_CPPFLAGS) -DLIB696
 
+lib751_SOURCES = lib751.c $(SUPPORTFILES) $(TESTUTIL) $(WARNLESS)
+lib751_LDADD = $(TESTUTIL_LIBS)
+
 lib1301_SOURCES = lib1301.c $(SUPPORTFILES) $(TESTUTIL)
 lib1301_LDADD = $(TESTUTIL_LIBS)
 
diff --git a/tests/libtest/lib751.c b/tests/libtest/lib751.c
new file mode 100644
index 0000000000..ab2f923b95
--- /dev/null
+++ b/tests/libtest/lib751.c
@@ -0,0 +1,92 @@
+/***************************************************************************
+ *                                  _   _ ____  _
+ *  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 "test.h"
+
+#include "testutil.h"
+#include "warnless.h"
+#include "memdebug.h"
+
+#define TEST_HANG_TIMEOUT 60 * 1000
+
+/*
+ * Get a single URL without select().
+ */
+
+CURLcode test(char *URL)
+{
+  CURL *easies[1000];
+  CURLM *m;
+  CURLcode res = CURLE_FAILED_INIT;
+  CURLMcode mres;
+  int i;
+
+  (void)URL;
+  memset(easies, 0, sizeof(easies));
+
+  curl_global_init(CURL_GLOBAL_DEFAULT);
+  m = curl_multi_init();
+  if(!m) {
+    res = CURLE_OUT_OF_MEMORY;
+    goto test_cleanup;
+  }
+
+  for(i = 0; i < 1000; i++) {
+    CURL *e = curl_easy_init();
+    if(!e) {
+      res = CURLE_OUT_OF_MEMORY;
+      goto test_cleanup;
+    }
+    easies[i] = e;
+
+    res = curl_easy_setopt(e, CURLOPT_URL, "https://www.example.com/");
+    if(!res)
+      res = curl_easy_setopt(e, CURLOPT_VERBOSE, 1L);
+    if(res)
+      goto test_cleanup;
+
+    mres = curl_multi_add_handle(m, e);
+    if(mres != CURLM_OK) {
+      printf("MULTI ERROR: %s\n", curl_multi_strerror(mres));
+      res = CURLE_FAILED_INIT;
+      goto test_cleanup;
+    }
+  }
+
+test_cleanup:
+
+  if(res)
+    printf("ERROR: %s\n", curl_easy_strerror(res));
+
+  for(i = 0; i < 1000; i++) {
+    if(easies[i]) {
+      curl_multi_add_handle(m, easies[i]);
+      curl_easy_cleanup(easies[i]);
+      easies[i] = NULL;
+    }
+  }
+  curl_multi_cleanup(m);
+  curl_global_cleanup();
+
+  return res;
+}