diff --git a/mysys/ma_dyncol.c b/mysys/ma_dyncol.c
index e0107a5601a18..ab25b04243986 100644
--- a/mysys/ma_dyncol.c
+++ b/mysys/ma_dyncol.c
@@ -773,7 +773,8 @@ dynamic_column_var_uint_get(uchar *data, size_t data_length,
   uint length;
   uchar *end= data + data_length;
 
-  for (length=0; data < end ; data++)
+  /* A 64-bit value needs at most 10 groups; stop before the shift reaches 64 */
+  for (length=0; data < end && length < 10; data++)
   {
     val+= (((ulonglong)((*data) & 0x7f)) << (length * 7));
     length++;
@@ -846,6 +847,10 @@ dynamic_column_uint_read(DYNAMIC_COLUMN_VALUE *store_it_here,
   ulonglong value= 0;
   size_t i;
 
+  /* an unsigned value occupies at most 8 bytes; reject the rest to keep i*8 < 64 */
+  if (length > 8)
+    return ER_DYNCOL_FORMAT;
+
   for (i= 0; i < length; i++)
     value+= ((ulonglong)data[i]) << (i*8);
 
@@ -906,8 +911,10 @@ static enum enum_dyncol_func_result
 dynamic_column_sint_read(DYNAMIC_COLUMN_VALUE *store_it_here,
                          uchar *data, size_t length)
 {
+  enum enum_dyncol_func_result rc;
   ulonglong val;
-  dynamic_column_uint_read(store_it_here, data, length);
+  if ((rc= dynamic_column_uint_read(store_it_here, data, length)))
+    return rc;
   val= store_it_here->x.ulong_value;
   if (val & 1)
     val= (val >> 1) ^ 0xffffffffffffffffULL;
diff --git a/unittest/mysys/ma_dyncol-t.c b/unittest/mysys/ma_dyncol-t.c
index 6e2c9b4c87ab4..34c93dba8a1c3 100644
--- a/unittest/mysys/ma_dyncol-t.c
+++ b/unittest/mysys/ma_dyncol-t.c
@@ -735,13 +735,48 @@ static void test_mdev_9773()
   mariadb_dyncol_free(&dynstr);
 }
 
+/*
+  A crafted record can give an integer column a data interval longer than the
+  8 bytes an integer occupies. The decoder used to shift by i*8 over that
+  interval, reaching a shift width of 64 (undefined, aborts under
+  -fsanitize=shift). Such a record must be rejected as ER_DYNCOL_FORMAT.
+*/
+static void test_overlong_int(DYNAMIC_COLUMN_TYPE type, const char *msg)
+{
+  DYNAMIC_COLUMN str;
+  DYNAMIC_COLUMN bad;
+  DYNAMIC_COLUMN_VALUE val, res;
+  uint column_nr= 1;
+  int rc;
+
+  val.type= type;
+  val.x.ulong_value= 1;
+
+  rc= mariadb_dyncol_create_many_num(&str, 1, &column_nr, &val, 1);
+  ok(rc == ER_DYNCOL_OK, "create %s", msg);
+
+  /* widen the single column's data interval past 8 bytes */
+  bad.length= str.length + 12;
+  bad.max_length= bad.length;
+  bad.alloc_increment= 0;
+  bad.str= (char *) malloc(bad.length);
+  memcpy(bad.str, str.str, str.length);
+  memset(bad.str + str.length, 0, 12);
+
+  rc= mariadb_dyncol_get_num(&bad, column_nr, &res);
+  ok(rc == ER_DYNCOL_FORMAT, "over-long %s rejected", msg);
+
+  free(bad.str);
+  mariadb_dyncol_free(&str);
+}
+
 int main(int argc __attribute__((unused)), char **argv)
 {
   uint i;
   char *big_string= (char *)malloc(1024*1024);
 
   MY_INIT(argv[0]);
-  plan(68);
+  plan(72);
 
   if (!big_string)
     exit(1);
@@ -875,6 +910,8 @@ int main(int argc __attribute__((unused)), char **argv)
   test_mdev_4994();
   test_mdev_4995();
   test_mdev_9773();
+  test_overlong_int(DYN_COL_UINT, "uint");
+  test_overlong_int(DYN_COL_INT, "sint");
 
   my_end(0);
   return exit_status();