diff --git a/src/MapUpdater.php b/src/MapUpdater.php
index 5683f839..e1f718a2 100644
--- a/src/MapUpdater.php
+++ b/src/MapUpdater.php
@@ -66,8 +66,8 @@ public function selectBaseMap(string $mapClass): MapUpdater
      * @return list<string>
      *   A list of error messages.
      *
-     * @throws \RuntimeException
-     *   If it was not possible to access the file.
+     * @throws SourceUpdateException
+     *   If it was not possible to access the source file.
      */
     public function loadMapFromApacheFile(string $source_file): array
     {
@@ -75,8 +75,7 @@ public function loadMapFromApacheFile(string $source_file): array
 
         $lines = @file($source_file);
         if ($lines == false) {
-            $errors[] = "Failed accessing {$source_file}";
-            return $errors;
+            throw new SourceUpdateException("Failed accessing {$source_file}");
         }
         $i = 1;
         foreach ($lines as $line) {
@@ -110,6 +109,9 @@ public function loadMapFromApacheFile(string $source_file): array
      *
      * @return list<string>
      *   A list of error messages.
+     *
+     * @throws SourceUpdateException
+     *   If it was not possible to access the source file.
      */
     public function loadMapFromFreedesktopFile(string $source_file): array
     {
@@ -117,8 +119,7 @@ public function loadMapFromFreedesktopFile(string $source_file): array
 
         $contents = @file_get_contents($source_file);
         if ($contents == false) {
-            $errors[] = 'Failed loading file ' . $source_file;
-            return $errors;
+            throw new SourceUpdateException('Failed loading file ' . $source_file);
         }
 
         $xml = @simplexml_load_string($contents);
diff --git a/src/SourceUpdateException.php b/src/SourceUpdateException.php
new file mode 100644
index 00000000..ff63f4e2
--- /dev/null
+++ b/src/SourceUpdateException.php
@@ -0,0 +1,10 @@
+<?php declare(strict_types=1);
+
+namespace FileEye\MimeMap;
+
+/**
+ * Exception thrown when data sources for map updates are not available.
+ */
+class SourceUpdateException extends \RuntimeException
+{
+}
diff --git a/tests/src/MapUpdaterTest.php b/tests/src/MapUpdaterTest.php
index f7b36daf..19d669f7 100644
--- a/tests/src/MapUpdaterTest.php
+++ b/tests/src/MapUpdaterTest.php
@@ -7,6 +7,7 @@
 use FileEye\MimeMap\Map\MiniMap;
 use FileEye\MimeMap\MapHandler;
 use FileEye\MimeMap\MapUpdater;
+use FileEye\MimeMap\SourceUpdateException;
 use PHPUnit\Framework\Attributes\BackupStaticProperties;
 use PHPUnit\Framework\Attributes\CoversClass;
 
@@ -57,17 +58,14 @@ public function testLoadMapFromApacheFile(): void
 
     public function testLoadMapFromApacheFileZeroLines(): void
     {
+        $this->expectException(SourceUpdateException::class);
         $this->updater->loadMapFromApacheFile(dirname(__FILE__) . '/../fixtures/zero.mime-types.txt');
-        // @phpstan-ignore method.impossibleType
-        $this->assertSame([], $this->newMap->getMapArray());
     }
 
     public function testLoadMapFromApacheMissingFile(): void
     {
-        $this->assertSame(
-            ["Failed accessing certainly_missing.xml"],
-            $this->updater->loadMapFromApacheFile('certainly_missing.xml')
-        );
+        $this->expectException(SourceUpdateException::class);
+        $this->updater->loadMapFromApacheFile('certainly_missing.txt');
     }
 
     public function testApplyOverridesFailure(): void
@@ -129,10 +127,8 @@ public function testLoadMapFromFreedesktopFileZeroLines(): void
 
     public function testLoadMapFromFreedesktopMissingFile(): void
     {
-        $this->assertSame(
-            ["Failed loading file certainly_missing.xml"],
-            $this->updater->loadMapFromFreedesktopFile('certainly_missing.xml')
-        );
+        $this->expectException(SourceUpdateException::class);
+        $this->updater->loadMapFromFreedesktopFile('certainly_missing.xml');
     }
 
     public function testLoadMapFromFreedesktopInvalidFile(): void