diff --git a/include/text.php b/include/text.php
index 775931c6ff..89c07000f7 100644
--- a/include/text.php
+++ b/include/text.php
@@ -72,22 +72,3 @@ function get_cats_and_terms($item)
 
 	return [$categories, $folders];
 }
-
-/// @TODO Rewrite this
-function is_a_date_arg($s) {
-	$i = intval($s);
-
-	if ($i > 1900) {
-		$y = date('Y');
-
-		if ($i <= $y + 1 && strpos($s, '-') == 4) {
-			$m = intval(substr($s, 5));
-
-			if ($m > 0 && $m <= 12) {
-				return true;
-			}
-		}
-	}
-
-	return false;
-}
diff --git a/mod/network.php b/mod/network.php
index 0438be7059..64f5cf505f 100644
--- a/mod/network.php
+++ b/mod/network.php
@@ -5,6 +5,7 @@
  */
 
 use Friendica\App;
+use Friendica\BaseObject;
 use Friendica\Content\Feature;
 use Friendica\Content\ForumManager;
 use Friendica\Content\Nav;
@@ -51,9 +52,12 @@ function network_init(App $a)
 		$group_id = 0;
 	}
 
+	/** @var DateTimeFormat $dtFormat */
+	$dtFormat = BaseObject::getClass(DateTimeFormat::class);
+
 	if ($a->argc > 1) {
 		for ($x = 1; $x < $a->argc; $x ++) {
-			if (is_a_date_arg($a->argv[$x])) {
+			if ($dtFormat->isYearMonth($a->argv[$x])) {
 				$is_a_date_query = true;
 				break;
 			}
@@ -461,9 +465,12 @@ function networkThreadedView(App $a, $update, $parent)
 
 	$default_permissions = [];
 
+	/** @var DateTimeFormat $dtFormat */
+	$dtFormat = BaseObject::getClass(DateTimeFormat::class);
+
 	if ($a->argc > 1) {
 		for ($x = 1; $x < $a->argc; $x ++) {
-			if (is_a_date_arg($a->argv[$x])) {
+			if ($dtFormat->isYearMonth($a->argv[$x])) {
 				if ($datequery) {
 					$datequery2 = Strings::escapeHtml($a->argv[$x]);
 				} else {
diff --git a/src/Module/Profile.php b/src/Module/Profile.php
index ed37540753..f38c77f2cd 100644
--- a/src/Module/Profile.php
+++ b/src/Module/Profile.php
@@ -131,9 +131,12 @@ class Profile extends BaseModule
 
 		$category = $datequery = $datequery2 = '';
 
+		/** @var DateTimeFormat $dtFormat */
+		$dtFormat = self::getClass(DateTimeFormat::class);
+
 		if ($a->argc > 2) {
 			for ($x = 2; $x < $a->argc; $x ++) {
-				if (is_a_date_arg($a->argv[$x])) {
+				if ($dtFormat->isYearMonth($a->argv[$x])) {
 					if ($datequery) {
 						$datequery2 = Strings::escapeHtml($a->argv[$x]);
 					} else {
diff --git a/src/Util/DateTimeFormat.php b/src/Util/DateTimeFormat.php
index 0b47a16f15..e29420e9ea 100644
--- a/src/Util/DateTimeFormat.php
+++ b/src/Util/DateTimeFormat.php
@@ -148,4 +148,37 @@ class DateTimeFormat
 
 		return $d->format($format);
 	}
+
+	/**
+	 * Checks, if the given string is a date with the pattern YYYY-MM
+	 *
+	 * @param string $dateString The given date
+	 *
+	 * @return boolean True, if the date is a valid pattern
+	 */
+	public function isYearMonth(string $dateString)
+	{
+		// Check format (2019-01, 2019-1, 2019-10)
+		if (!preg_match('/^([12]\d{3}-(1[0-2]|0[1-9]|\d))$/', $dateString)) {
+			return false;
+		}
+
+		$date = DateTime::createFromFormat('Y-m', $dateString);
+
+		if (!$date) {
+			return false;
+		}
+
+		try {
+			$now = new DateTime();
+		} catch (\Throwable $t) {
+			return false;
+		}
+
+		if ($date > $now) {
+			return false;
+		}
+
+		return true;
+	}
 }
diff --git a/tests/src/Util/DateTimeFormatTest.php b/tests/src/Util/DateTimeFormatTest.php
new file mode 100644
index 0000000000..bdc902eab2
--- /dev/null
+++ b/tests/src/Util/DateTimeFormatTest.php
@@ -0,0 +1,61 @@
+<?php
+
+namespace Friendica\Test\src\Util;
+
+use Friendica\Test\MockedTest;
+use Friendica\Util\DateTimeFormat;
+
+class DateTimeFormatTest extends MockedTest
+{
+	public function dataYearMonth()
+	{
+		return [
+			'validNormal' => [
+				'input' => '1990-10',
+				'assert' => true,
+			],
+			'validOneCharMonth' => [
+				'input' => '1990-1',
+				'assert' => true,
+			],
+			'validTwoCharMonth' => [
+				'input' => '1990-01',
+				'assert' => true,
+			],
+			'invalidFormat' => [
+				'input' => '199-11',
+				'assert' => false,
+			],
+			'invalidFormat2' => [
+				'input' => '1990-15',
+				'assert' => false,
+			],
+			'invalidFormat3' => [
+				'input' => '99-101',
+				'assert' => false,
+			],
+			'invalidFormat4' => [
+				'input' => '11-1990',
+				'assert' => false,
+			],
+			'invalidFuture' => [
+				'input' => '3030-12',
+				'assert' => false,
+			],
+			'invalidYear' => [
+				'input' => '-100-10',
+				'assert' => false,
+			],
+		];
+	}
+
+	/**
+	 * @dataProvider dataYearMonth
+	 */
+	public function testIsYearMonth(string $input, bool $assert)
+	{
+		$dtFormat = new DateTimeFormat();
+
+		$this->assertEquals($assert, $dtFormat->isYearMonth($input));
+	}
+}