diff --git a/src/wallet/db.cpp b/src/wallet/db.cpp
--- a/src/wallet/db.cpp
+++ b/src/wallet/db.cpp
@@ -21,6 +21,46 @@
 #include <sys/stat.h>
 #endif
 
+namespace {
+//! Make sure database has a unique fileid within the environment. If it
+//! doesn't, throw an error. BDB caches do not work properly when more than one
+//! open database has the same fileid (values written to one database may show
+//! up in reads to other databases).
+//!
+//! BerkeleyDB generates unique fileids by default
+//! (https://docs.oracle.com/cd/E17275_01/html/programmer_reference/program_copy.html),
+//! so bitcoin should never create different databases with the same fileid, but
+//! this error can be triggered if users manually copy database files.
+void CheckUniqueFileid(const CDBEnv &env, const std::string &filename, Db &db) {
+    if (env.IsMock()) {
+        return;
+    }
+
+    u_int8_t fileid[DB_FILE_ID_LEN];
+    int ret = db.get_mpf()->get_fileid(fileid);
+    if (ret != 0) {
+        throw std::runtime_error(
+            strprintf("CDB: Can't open database %s (get_fileid failed with %d)",
+                      filename, ret));
+    }
+
+    for (const auto &item : env.mapDb) {
+        u_int8_t item_fileid[DB_FILE_ID_LEN];
+        if (item.second &&
+            item.second->get_mpf()->get_fileid(item_fileid) == 0 &&
+            memcmp(fileid, item_fileid, sizeof(fileid)) == 0) {
+            const char *item_filename = nullptr;
+            item.second->get_dbname(&item_filename, nullptr);
+            throw std::runtime_error(strprintf(
+                "CDB: Can't open database %s (duplicates fileid %s from %s)",
+                filename,
+                HexStr(std::begin(item_fileid), std::end(item_fileid)),
+                item_filename ? item_filename : "(unknown database)"));
+        }
+    }
+}
+} // namespace
+
 //
 // CDB
 //
@@ -423,6 +463,7 @@
                 throw std::runtime_error(strprintf(
                     "CDB: Error %d, can't open database %s", ret, strFilename));
             }
+            CheckUniqueFileid(*env, strFilename, *pdb_temp);
 
             pdb = pdb_temp.release();
             env->mapDb[strFilename] = pdb;
diff --git a/test/functional/multiwallet.py b/test/functional/multiwallet.py
--- a/test/functional/multiwallet.py
+++ b/test/functional/multiwallet.py
@@ -7,6 +7,7 @@
 Verify that a bitcoind node can load multiple wallet files
 """
 import os
+import shutil
 
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import assert_equal, assert_raises_rpc_error
@@ -32,6 +33,12 @@
         self.assert_start_raises_init_error(
             0, ['-wallet=w11'], 'Error loading wallet w11. -wallet filename must be a regular file.')
 
+        # should not initialize if one wallet is a copy of another
+        shutil.copyfile(os.path.join(self.options.tmpdir, 'node0', 'regtest', 'w2'),
+                        os.path.join(self.options.tmpdir, 'node0', 'regtest', 'w22'))
+        self.assert_start_raises_init_error(
+            0, ['-wallet=w2', '-wallet=w22'], 'duplicates fileid')
+
         # should not initialize if wallet file is a symlink
         wallet_dir = os.path.abspath(os.path.join(
             self.options.tmpdir, 'node0', 'regtest'))