diff --git a/apps/theming/css/theming.scss b/apps/theming/css/theming.scss
index 2d0afa2d298dc..ac303f61a6b7f 100644
--- a/apps/theming/css/theming.scss
+++ b/apps/theming/css/theming.scss
@@ -44,8 +44,10 @@
 /* override styles for login screen in guest.css */
 #header .logo,
 #header .logo-icon {
-	background-size: contain;
 	background-image: url(#{$image-logo});
+	@if $theming-logo-mime != '' {
+		background-size: contain;
+	}
 }
 
 #body-login,
@@ -111,4 +113,4 @@ input.primary {
 			}
 		}
 	}
-}
\ No newline at end of file
+}
diff --git a/apps/theming/lib/ThemingDefaults.php b/apps/theming/lib/ThemingDefaults.php
index 0824a36ccdce2..2b3be1e641320 100644
--- a/apps/theming/lib/ThemingDefaults.php
+++ b/apps/theming/lib/ThemingDefaults.php
@@ -192,6 +192,8 @@ public function getScssVariables() {
 
 		$variables = [
 			'theming-cachebuster' => "'" . $this->config->getAppValue('theming', 'cachebuster', '0') . "'",
+			'theming-logo-mime' => "'" . $this->config->getAppValue('theming', 'logoMime', '') . "'",
+			'theming-background-mime' => "'" . $this->config->getAppValue('theming', 'backgroundMime', '') . "'"
 		];
 
 		$variables['image-logo'] = "'".$this->urlGenerator->getAbsoluteURL($this->getLogo())."'";
diff --git a/apps/theming/tests/ThemingDefaultsTest.php b/apps/theming/tests/ThemingDefaultsTest.php
index a7cb7790aa65b..8646eaf865f80 100644
--- a/apps/theming/tests/ThemingDefaultsTest.php
+++ b/apps/theming/tests/ThemingDefaultsTest.php
@@ -499,12 +499,14 @@ public function testGetScssVariablesCached() {
 	public function testGetScssVariables() {
 		$this->config->expects($this->at(0))->method('getAppValue')->with('theming', 'cachebuster', '0')->willReturn('0');
 		$this->config->expects($this->at(1))->method('getAppValue')->with('theming', 'logoMime', false)->willReturn('jpeg');
-		$this->config->expects($this->at(2))->method('getAppValue')->with('theming', 'cachebuster', '0')->willReturn('0');
-		$this->config->expects($this->at(3))->method('getAppValue')->with('theming', 'backgroundMime', false)->willReturn('jpeg');
+		$this->config->expects($this->at(2))->method('getAppValue')->with('theming', 'backgroundMime', false)->willReturn('jpeg');
+		$this->config->expects($this->at(3))->method('getAppValue')->with('theming', 'logoMime', false)->willReturn('jpeg');
 		$this->config->expects($this->at(4))->method('getAppValue')->with('theming', 'cachebuster', '0')->willReturn('0');
-		$this->config->expects($this->at(5))->method('getAppValue')->with('theming', 'color', null)->willReturn($this->defaults->getColorPrimary());
-		$this->config->expects($this->at(6))->method('getAppValue')->with('theming', 'color', $this->defaults->getColorPrimary())->willReturn($this->defaults->getColorPrimary());
-		$this->config->expects($this->at(7))->method('getAppValue')->with('theming', 'color', $this->defaults->getColorPrimary())->willReturn($this->defaults->getColorPrimary());
+		$this->config->expects($this->at(5))->method('getAppValue')->with('theming', 'backgroundMime', false)->willReturn('jpeg');
+		$this->config->expects($this->at(6))->method('getAppValue')->with('theming', 'cachebuster', '0')->willReturn('0');
+		$this->config->expects($this->at(7))->method('getAppValue')->with('theming', 'color', null)->willReturn($this->defaults->getColorPrimary());
+		$this->config->expects($this->at(8))->method('getAppValue')->with('theming', 'color', $this->defaults->getColorPrimary())->willReturn($this->defaults->getColorPrimary());
+		$this->config->expects($this->at(9))->method('getAppValue')->with('theming', 'color', $this->defaults->getColorPrimary())->willReturn($this->defaults->getColorPrimary());
 
 		$this->util->expects($this->any())->method('invertTextColor')->with($this->defaults->getColorPrimary())->willReturn(false);
 		$this->cache->expects($this->once())->method('get')->with('getScssVariables')->willReturn(null);
@@ -530,6 +532,8 @@ public function testGetScssVariables() {
 
 		$expected = [
 			'theming-cachebuster' => '\'0\'',
+			'theming-logo-mime' => '\'jpeg\'',
+			'theming-background-mime' => '\'jpeg\'',
 			'image-logo' => "'absolute-custom-logo?v=0'",
 			'image-login-background' => "'absolute-custom-background?v=0'",
 			'color-primary' => $this->defaults->getColorPrimary(),