diff --git a/Sources/Db/APIs/MySQL.php b/Sources/Db/APIs/MySQL.php
index 625e43d520..389b2c6027 100644
--- a/Sources/Db/APIs/MySQL.php
+++ b/Sources/Db/APIs/MySQL.php
@@ -361,9 +361,21 @@ public function insert(string $method, string $table, array $columns, array $dat
 			}
 		}
 
-		// Inserting data as a single row can be done as a single array.
-		if (!is_array($data[array_rand($data)])) {
-			$data = [$data];
+		// Ensure that $data is a multidimensional array.
+		if (array_filter($data, fn($dataRow) => is_array($dataRow)) !== $data) {
+			// If backward compatibility mode is enabled, quietly clean up after
+			// old mods that did the wrong thing. Otherwise, trigger an error.
+			if (!empty(Config::$backward_compatibility)) {
+				$data = [$data];
+			} else {
+				$this->error_backtrace(
+					'Invalid data structure sent to the database.',
+					'',
+					E_USER_ERROR,
+					__FILE__,
+					__LINE__,
+				);
+			}
 		}
 
 		// Create the mold for a single row insert.
diff --git a/Sources/Db/APIs/PostgreSQL.php b/Sources/Db/APIs/PostgreSQL.php
index c9420bc34d..1aef375f1f 100644
--- a/Sources/Db/APIs/PostgreSQL.php
+++ b/Sources/Db/APIs/PostgreSQL.php
@@ -387,8 +387,21 @@ public function insert(string $method, string $table, array $columns, array $dat
 		// Force method to lower case
 		$method = strtolower($method);
 
-		if (!is_array($data[array_rand($data)])) {
-			$data = [$data];
+		// Ensure that $data is a multidimensional array.
+		if (array_filter($data, fn($dataRow) => is_array($dataRow)) !== $data) {
+			// If backward compatibility mode is enabled, quietly clean up after
+			// old mods that did the wrong thing. Otherwise, trigger an error.
+			if (!empty(Config::$backward_compatibility)) {
+				$data = [$data];
+			} else {
+				$this->error_backtrace(
+					'Invalid data structure sent to the database.',
+					'',
+					E_USER_ERROR,
+					__FILE__,
+					__LINE__,
+				);
+			}
 		}
 
 		// Replace the prefix holder with the actual prefix.
diff --git a/Sources/Db/DatabaseApiInterface.php b/Sources/Db/DatabaseApiInterface.php
index 821e25c801..fc40a8b5e0 100644
--- a/Sources/Db/DatabaseApiInterface.php
+++ b/Sources/Db/DatabaseApiInterface.php
@@ -71,16 +71,23 @@ public function fetch_all(object $request): array;
 	public function free_result(object $result): bool;
 
 	/**
-	 * Gets the ID of the most recently inserted row.
+	 * Inserts one or more rows of data into a database table and optionally
+	 * returns the resulting IDs.
 	 *
 	 * @param string $method INSERT or REPLACE.
 	 * @param string $table The table (only used for Postgres).
-	 * @param array $columns An array of the columns we're inserting the data into. Should contain 'column' => 'datatype' pairs.
-	 * @param array $data The data to insert.
-	 * @param array $keys The keys for the table, needs to be not empty on replace mode.
-	 * @param object $connection = null The connection (if null, $db_connection is used).
-	 * @param int returnmode 0 = nothing(default), 1 = last row id, 2 = all rows id as array.
-	 * @return int The ID of the most recently inserted row.
+	 * @param array $columns Array of the columns we're inserting the data into.
+	 *    Should contain 'column' => 'datatype' pairs.
+	 * @param array $data Rows of data to insert. Each element of $data must
+	 *    be an array of values corresponding to $columns.
+	 * @param array $keys The keys for the table. Must not empty in replace mode.
+	 * @param int $returnmode 0 = nothing, 1 = last row ID, 2 = all row IDs.
+	 *    Default: 0.
+	 * @param object $connection The connection to use.
+	 *    If null, $db_connection is used.
+	 * @return int|array|null Null if $returnmode is 0, the ID of the most
+	 *    recently inserted row if $returnmode is 1, or the IDS of all the
+	 *    inserted rows if $returnmode is 2.
 	 */
 	public function insert(string $method, string $table, array $columns, array $data, array $keys, int $returnmode = 0, ?object $connection = null): int|array|null;