diff --git a/src/Logger/FilteredLogLevelDecorator.php b/src/Logger/FilteredLogLevelDecorator.php
index 3d653373..658279f4 100644
--- a/src/Logger/FilteredLogLevelDecorator.php
+++ b/src/Logger/FilteredLogLevelDecorator.php
@@ -7,6 +7,7 @@
 use Psr\Log\LoggerInterface;
 use Psr\Log\LoggerTrait;
 use Psr\Log\LogLevel;
+use Throwable;
 use Webmozart\Assert\Assert;
 
 use function array_keys;
@@ -45,15 +46,24 @@ final class FilteredLogLevelDecorator implements LoggerInterface
      */
     public function __construct(LoggerInterface $realLogger, string $minimumLogLevel)
     {
-        Assert::keyExists(
-            self::LOG_LEVEL_ORDER,
-            strtolower($minimumLogLevel),
-            sprintf(
-                'Log level %s was not a valid PSR-3 compatible log level. Should be one of: %s',
-                $minimumLogLevel,
-                implode(', ', array_keys(self::LOG_LEVEL_ORDER))
-            )
-        );
+        try {
+            Assert::keyExists(
+                self::LOG_LEVEL_ORDER,
+                strtolower($minimumLogLevel),
+                sprintf(
+                    'Log level %s was not a valid PSR-3 compatible log level. Should be one of: %s',
+                    $minimumLogLevel,
+                    implode(', ', array_keys(self::LOG_LEVEL_ORDER))
+                )
+            );
+        } catch (Throwable $e) {
+            $minimumLogLevel = LogLevel::DEBUG;
+            $realLogger->log(
+                LogLevel::ERROR,
+                $e->getMessage(),
+                ['exception' => $e]
+            );
+        }
 
         $this->minimumLogLevel = self::LOG_LEVEL_ORDER[strtolower($minimumLogLevel)];
         $this->realLogger      = $realLogger;
diff --git a/tests/Unit/Logger/FilteredLogLevelDecoratorTest.php b/tests/Unit/Logger/FilteredLogLevelDecoratorTest.php
index c4ac73a6..8c09d756 100644
--- a/tests/Unit/Logger/FilteredLogLevelDecoratorTest.php
+++ b/tests/Unit/Logger/FilteredLogLevelDecoratorTest.php
@@ -4,7 +4,6 @@
 
 namespace Scoutapm\UnitTests\Logger;
 
-use InvalidArgumentException;
 use PHPUnit\Framework\MockObject\MockObject;
 use PHPUnit\Framework\TestCase;
 use Psr\Log\LoggerInterface;
@@ -31,11 +30,16 @@ public function setUp(): void
 
     public function testInvalidLogLevelStringGivesClearErrorMessage(): void
     {
-        $this->expectException(InvalidArgumentException::class);
-        $this->expectExceptionMessage(
-            'Log level foo was not a valid PSR-3 compatible log level. '
-            . 'Should be one of: debug, info, notice, warning, error, critical, alert, emergency'
-        );
+        $this->decoratedLogger
+            ->expects(self::once())
+            ->method('log')
+            ->with(
+                LogLevel::ERROR,
+                'Log level foo was not a valid PSR-3 compatible log level. '
+                . 'Should be one of: debug, info, notice, warning, error, critical, alert, emergency',
+                self::anything()
+            );
+
         new FilteredLogLevelDecorator($this->decoratedLogger, 'foo');
     }
 
@@ -99,9 +103,36 @@ public function invalidLogLevelProvider(): array
     }
 
     /** @dataProvider invalidLogLevelProvider */
-    public function testInvalidLogLevelsAreRejected(string $invalidLogLevel): void
+    public function testInvalidLogLevelsAreLoggedAsErrors(string $invalidLogLevel): void
     {
-        $this->expectException(InvalidArgumentException::class);
+        $this->decoratedLogger
+            ->expects(self::once())
+            ->method('log')
+            ->with(
+                LogLevel::ERROR,
+                self::stringContains($invalidLogLevel . ' was not a valid PSR-3'),
+                self::anything()
+            );
+
         new FilteredLogLevelDecorator($this->decoratedLogger, $invalidLogLevel);
     }
+
+    /** @dataProvider invalidLogLevelProvider */
+    public function testInvalidLogLevelsDefaultToDebug(string $invalidLogLevel): void
+    {
+        $decorator = new FilteredLogLevelDecorator($this->decoratedLogger, $invalidLogLevel);
+
+        $message = 'info message';
+
+        $this->decoratedLogger
+            ->expects(self::once())
+            ->method('log')
+            ->with(
+                LogLevel::DEBUG,
+                self::stringContains($message),
+                self::anything()
+            );
+
+        $decorator->debug($message);
+    }
 }