diff --git a/lib/dml/mssql_native_moodle_database.php b/lib/dml/mssql_native_moodle_database.php
index 18e76812dcb..6e8b3577e69 100644
--- a/lib/dml/mssql_native_moodle_database.php
+++ b/lib/dml/mssql_native_moodle_database.php
@@ -351,10 +351,12 @@ class mssql_native_moodle_database extends moodle_database {
         if ($result) {
             while ($row = mssql_fetch_row($result)) {
                 $tablename = reset($row);
-                if (strpos($tablename, $this->prefix) !== 0) {
-                    continue;
+                if ($this->prefix !== '') {
+                    if (strpos($tablename, $this->prefix) !== 0) {
+                        continue;
+                    }
+                    $tablename = substr($tablename, strlen($this->prefix));
                 }
-                $tablename = substr($tablename, strlen($this->prefix));
                 $this->tables[$tablename] = $tablename;
             }
             $this->free_result($result);
diff --git a/lib/dml/oci_native_moodle_database.php b/lib/dml/oci_native_moodle_database.php
index 8beaf21d2a1..a529277b1e8 100644
--- a/lib/dml/oci_native_moodle_database.php
+++ b/lib/dml/oci_native_moodle_database.php
@@ -419,10 +419,12 @@ class oci_native_moodle_database extends moodle_database {
         oci_free_statement($stmt);
         $records = array_map('strtolower', $records['TABLE_NAME']);
         foreach ($records as $tablename) {
-            if (strpos($tablename, $this->prefix) !== 0) {
-                continue;
+            if ($this->prefix !== '') {
+                if (strpos($tablename, $this->prefix) !== 0) {
+                    continue;
+                }
+                $tablename = substr($tablename, strlen($this->prefix));
             }
-            $tablename = substr($tablename, strlen($this->prefix));
             $this->tables[$tablename] = $tablename;
         }
 
diff --git a/lib/dml/pgsql_native_moodle_database.php b/lib/dml/pgsql_native_moodle_database.php
index 7262f65a5f6..3d9771dfcd1 100644
--- a/lib/dml/pgsql_native_moodle_database.php
+++ b/lib/dml/pgsql_native_moodle_database.php
@@ -297,10 +297,12 @@ class pgsql_native_moodle_database extends moodle_database {
         if ($result) {
             while ($row = pg_fetch_row($result)) {
                 $tablename = reset($row);
-                if (strpos($tablename, $this->prefix) !== 0) {
-                    continue;
+                if ($this->prefix !== '') {
+                    if (strpos($tablename, $this->prefix) !== 0) {
+                        continue;
+                    }
+                    $tablename = substr($tablename, strlen($this->prefix));
                 }
-                $tablename = substr($tablename, strlen($this->prefix));
                 $this->tables[$tablename] = $tablename;
             }
             pg_free_result($result);
diff --git a/lib/dml/sqlite3_pdo_moodle_database.php b/lib/dml/sqlite3_pdo_moodle_database.php
index 01731fc6c4a..c52b2f1916a 100644
--- a/lib/dml/sqlite3_pdo_moodle_database.php
+++ b/lib/dml/sqlite3_pdo_moodle_database.php
@@ -152,10 +152,13 @@ class sqlite3_pdo_moodle_database extends pdo_moodle_database {
         foreach ($rstables as $table) {
             $table = $table['name'];
             $table = strtolower($table);
-            if (empty($this->prefix) || strpos($table, $this->prefix) === 0) {
+            if ($this->prefix !== '') {
+                if (strpos($table, $this->prefix) !== 0) {
+                    continue;
+                }
                 $table = substr($table, strlen($this->prefix));
-                $tables[$table] = $table;
             }
+            $tables[$table] = $table;
         }
         return $tables;
     }
diff --git a/lib/dml/sqlsrv_native_moodle_database.php b/lib/dml/sqlsrv_native_moodle_database.php
index 2147e6c0a6c..5fe2ab2107d 100644
--- a/lib/dml/sqlsrv_native_moodle_database.php
+++ b/lib/dml/sqlsrv_native_moodle_database.php
@@ -401,10 +401,12 @@ class sqlsrv_native_moodle_database extends moodle_database {
         if ($result) {
             while ($row = sqlsrv_fetch_array($result)) {
                 $tablename = reset($row);
-                if (strpos($tablename, $this->prefix) !== 0) {
-                    continue;
+                if ($this->prefix !== '') {
+                    if (strpos($tablename, $this->prefix) !== 0) {
+                        continue;
+                    }
+                    $tablename = substr($tablename, strlen($this->prefix));
                 }
-                $tablename = substr($tablename, strlen($this->prefix));
                 $this->tables[$tablename] = $tablename;
             }
             $this->free_result($result);