diff --git a/src/Psalm/Internal/Type/Comparator/ScalarTypeComparator.php b/src/Psalm/Internal/Type/Comparator/ScalarTypeComparator.php
index f3dc6a63c..9df93389b 100644
--- a/src/Psalm/Internal/Type/Comparator/ScalarTypeComparator.php
+++ b/src/Psalm/Internal/Type/Comparator/ScalarTypeComparator.php
@@ -585,6 +585,11 @@ class ScalarTypeComparator
             return true;
         }
 
+        if ($input_type_part instanceof TLowercaseString
+            && get_class($container_type_part) === TNonEmptyString::class) {
+            return false;
+        }
+
         if ($input_type_part->getKey() === $container_type_part->getKey()) {
             return true;
         }
diff --git a/tests/Template/ConditionalReturnTypeTest.php b/tests/Template/ConditionalReturnTypeTest.php
index 0cbab4dc0..211dc000e 100644
--- a/tests/Template/ConditionalReturnTypeTest.php
+++ b/tests/Template/ConditionalReturnTypeTest.php
@@ -841,6 +841,24 @@ class ConditionalReturnTypeTest extends TestCase
                     }
                     '
             ],
+            'strlenReturnsIntForLowercaseString' => [
+                '<?php
+                    /**
+                     * @psalm-return (
+                     *     $string is non-empty-string
+                     *     ? positive-int
+                     *     : int
+                     * )
+                     */
+                    function strlen2(string $string) : int { return 1;}
+
+                    function test(string $s): void {
+                        if (strlen2(strtolower($s))) {
+                            echo 1;
+                        }
+                    }
+                    '
+            ],
         ];
     }
 }