diff --git a/Sources/Subs-Calendar.php b/Sources/Subs-Calendar.php
index f4b2cdbf4a..b69ef57047 100644
--- a/Sources/Subs-Calendar.php
+++ b/Sources/Subs-Calendar.php
@@ -1882,8 +1882,11 @@ function convertDateToEnglish($date)
 		'Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat'
 	));
 	// Find all possible variants of AM and PM for this language.
-	$replacements[strtolower($txt['time_am'])] = 'AM';
-	$replacements[strtolower($txt['time_pm'])] = 'PM';
+	if (trim($txt['time_am']) !== '' && trim($txt['time_pm']) !== '')
+	{
+		$replacements[strtolower($txt['time_am'])] = 'AM';
+		$replacements[strtolower($txt['time_pm'])] = 'PM';
+	}
 	if (($am = smf_strftime('%p', strtotime('01:00:00'))) !== 'p' && $am !== false)
 	{
 		$replacements[strtolower($am)] = 'AM';