diff --git a/classes/handler/public.php b/classes/handler/public.php
index 190c806be..c6ec39f36 100755
--- a/classes/handler/public.php
+++ b/classes/handler/public.php
@@ -381,7 +381,7 @@ class Handler_Public extends Handler {
 			$login = clean($_POST["login"]);
 			$password = clean($_POST["password"]);
 			$remember_me = clean($_POST["remember_me"] ?? false);
-			$safe_mode = checkbox_to_sql_bool(clean($_POST["safe_mode"] ?? false));
+			$safe_mode = checkbox_to_sql_bool($_POST["safe_mode"] ?? false);
 
 			if (session_status() != PHP_SESSION_ACTIVE) {
 				if ($remember_me) {
diff --git a/classes/pref/feeds.php b/classes/pref/feeds.php
index d2fcdc804..679eb12e9 100755
--- a/classes/pref/feeds.php
+++ b/classes/pref/feeds.php
@@ -713,12 +713,12 @@ class Pref_Feeds extends Handler_Protected {
 		$cat_id = (int) clean($_POST["cat_id"] ?? 0);
 		$auth_login = clean($_POST["auth_login"] ?? "");
 		$auth_pass = clean($_POST["auth_pass"] ?? "");
-		$private = clean($_POST["private"] ?? "") == "on";
-		$include_in_digest = clean($_POST["include_in_digest"] ?? "") == "on";
-		$cache_images = clean($_POST["cache_images"] ?? "") == "on";
-		$hide_images = clean($_POST["hide_images"] ?? "") == "on";
-		$always_display_enclosures = clean($_POST["always_display_enclosures"] ?? "") == "on";
-		$mark_unread_on_update = clean($_POST["mark_unread_on_update"] ?? "") == "on";
+		$private = checkbox_to_sql_bool($_POST["private"] ?? "");
+		$include_in_digest = checkbox_to_sql_bool($_POST["include_in_digest"] ?? "");
+		$cache_images = checkbox_to_sql_bool($_POST["cache_images"] ?? "");
+		$hide_images = checkbox_to_sql_bool($_POST["hide_images"] ?? "");
+		$always_display_enclosures = checkbox_to_sql_bool($_POST["always_display_enclosures"] ?? "");
+		$mark_unread_on_update = checkbox_to_sql_bool($_POST["mark_unread_on_update"] ?? "");
 
 		$feed_language = clean($_POST["feed_language"] ?? "");
 
diff --git a/classes/pref/filters.php b/classes/pref/filters.php
index 19ec8d39e..2656c0370 100755
--- a/classes/pref/filters.php
+++ b/classes/pref/filters.php
@@ -57,8 +57,8 @@ class Pref_Filters extends Handler_Protected {
 		$filter = array();
 
 		$filter["enabled"] = true;
-		$filter["match_any_rule"] = checkbox_to_sql_bool(clean($_REQUEST["match_any_rule"] ?? false));
-		$filter["inverse"] = checkbox_to_sql_bool(clean($_REQUEST["inverse"] ?? false));
+		$filter["match_any_rule"] = checkbox_to_sql_bool($_REQUEST["match_any_rule"] ?? false);
+		$filter["inverse"] = checkbox_to_sql_bool($_REQUEST["inverse"] ?? false);
 
 		$filter["rules"] = array();
 		$filter["actions"] = array("dummy-action");
@@ -511,9 +511,9 @@ class Pref_Filters extends Handler_Protected {
 
 	function editSave(): void {
 		$filter_id = (int) clean($_REQUEST["id"]);
-		$enabled = checkbox_to_sql_bool(clean($_REQUEST["enabled"] ?? false));
-		$match_any_rule = checkbox_to_sql_bool(clean($_REQUEST["match_any_rule"] ?? false));
-		$inverse = checkbox_to_sql_bool(clean($_REQUEST["inverse"] ?? false));
+		$enabled = checkbox_to_sql_bool($_REQUEST["enabled"] ?? false);
+		$match_any_rule = checkbox_to_sql_bool($_REQUEST["match_any_rule"] ?? false);
+		$inverse = checkbox_to_sql_bool($_REQUEST["inverse"] ?? false);
 		$title = clean($_REQUEST["title"]);
 
 		$this->pdo->beginTransaction();
@@ -624,10 +624,10 @@ class Pref_Filters extends Handler_Protected {
 	}
 
 	function add(): void {
-		$enabled = checkbox_to_sql_bool(clean($_REQUEST["enabled"] ?? false));
-		$match_any_rule = checkbox_to_sql_bool(clean($_REQUEST["match_any_rule"] ?? false));
+		$enabled = checkbox_to_sql_bool($_REQUEST["enabled"] ?? false);
+		$match_any_rule = checkbox_to_sql_bool($_REQUEST["match_any_rule"] ?? false);
 		$title = clean($_REQUEST["title"]);
-		$inverse = checkbox_to_sql_bool(clean($_REQUEST["inverse"] ?? false));
+		$inverse = checkbox_to_sql_bool($_REQUEST["inverse"] ?? false);
 
 		$this->pdo->beginTransaction();
 
diff --git a/include/functions.php b/include/functions.php
index 403c96b85..0d7f8c756 100644
--- a/include/functions.php
+++ b/include/functions.php
@@ -357,9 +357,11 @@
 		return $s && ($s !== "f" && $s !== "false"); //no-op for PDO, backwards compat for legacy layer
 	}
 
-	/** @deprecated misleading name, seems to be pointless wrapper */
+	/** workaround for PDO casting all query parameters to string unless type is specified explicitly,
+	 * which breaks booleans having false value because they become empty string literals ("") causing
+	 * DB type mismatches and breaking SQL queries */
 	function bool_to_sql_bool(bool $s): int {
-		return $s ? 1 : 0;
+		return (int)$s;
 	}
 
 	function file_is_locked(string $filename): bool {
@@ -411,12 +413,13 @@
 		}
 	}
 
-	/**
+	/** checkbox-specific workaround for PDO casting all query parameters to string unless type is
+	 * specified explicitly, which breaks booleans having false value because they become empty
+	 * string literals ("") causing DB type mismatches and breaking SQL queries
 	 * @param mixed $val
-	 * @deprecated misleading name, seems to be a pointless wrapper
 	 */
 	function checkbox_to_sql_bool($val): int {
-		return ($val == "on") ? 1 : 0;
+		return ($val === "on") ? 1 : 0;
 	}
 
 	function uniqid_short(): string {