diff --git a/src/Type/Php/StrCaseFunctionsReturnTypeExtension.php b/src/Type/Php/StrCaseFunctionsReturnTypeExtension.php
index db36561ab6..c6226f5a5f 100644
--- a/src/Type/Php/StrCaseFunctionsReturnTypeExtension.php
+++ b/src/Type/Php/StrCaseFunctionsReturnTypeExtension.php
@@ -142,18 +142,19 @@ public function getTypeFromFunctionCall(
 		}
 
 		$accessoryTypes = [];
-		if ($forceLowercase || ($keepLowercase && $argType->isLowercaseString()->yes())) {
+		$argStringType = $argType->toString();
+		if ($forceLowercase || ($keepLowercase && $argStringType->isLowercaseString()->yes())) {
 			$accessoryTypes[] = new AccessoryLowercaseStringType();
 		}
-		if ($forceUppercase || ($keepUppercase && $argType->isUppercaseString()->yes())) {
+		if ($forceUppercase || ($keepUppercase && $argStringType->isUppercaseString()->yes())) {
 			$accessoryTypes[] = new AccessoryUppercaseStringType();
 		}
 
-		if ($argType->isNumericString()->yes()) {
+		if ($argStringType->isNumericString()->yes()) {
 			$accessoryTypes[] = new AccessoryNumericStringType();
-		} elseif ($argType->isNonFalsyString()->yes()) {
+		} elseif ($argStringType->isNonFalsyString()->yes()) {
 			$accessoryTypes[] = new AccessoryNonFalsyStringType();
-		} elseif ($argType->isNonEmptyString()->yes()) {
+		} elseif ($argStringType->isNonEmptyString()->yes()) {
 			$accessoryTypes[] = new AccessoryNonEmptyStringType();
 		}
 
diff --git a/tests/PHPStan/Analyser/nsrt/non-falsy-string.php b/tests/PHPStan/Analyser/nsrt/non-falsy-string.php
index c5fd9fc1d8..598a358927 100644
--- a/tests/PHPStan/Analyser/nsrt/non-falsy-string.php
+++ b/tests/PHPStan/Analyser/nsrt/non-falsy-string.php
@@ -87,6 +87,7 @@ function stringFunctions(string $s, $nonFalsey, $arrayOfNonFalsey, $nonEmptyArra
 		assertType('non-falsy-string', escapeshellarg($nonFalsey));
 		assertType('non-falsy-string', escapeshellcmd($nonFalsey));
 
+		assertType('non-falsy-string&uppercase-string', strtoupper($s ?: 1));
 		assertType('non-falsy-string&uppercase-string', strtoupper($nonFalsey));
 		assertType('lowercase-string&non-falsy-string', strtolower($nonFalsey));
 		assertType('non-falsy-string&uppercase-string', mb_strtoupper($nonFalsey));