diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3994bec7..23f8c0a3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,9 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+### `jsonschema-generator`
+#### Fixed
+- avoid error being thrown in `allOf` clean-up for invalid payload
 
 ## [4.31.0] - 2023-04-22
 ### `jsonschema-generator`
diff --git a/jsonschema-generator/src/main/java/com/github/victools/jsonschema/generator/impl/SchemaCleanUpUtils.java b/jsonschema-generator/src/main/java/com/github/victools/jsonschema/generator/impl/SchemaCleanUpUtils.java
index a31c1314..d6d450c4 100644
--- a/jsonschema-generator/src/main/java/com/github/victools/jsonschema/generator/impl/SchemaCleanUpUtils.java
+++ b/jsonschema-generator/src/main/java/com/github/victools/jsonschema/generator/impl/SchemaCleanUpUtils.java
@@ -386,8 +386,13 @@ private Supplier<JsonNode> returnOverlapOfStringsOrStringArrays(List<JsonNode> n
                 // invalid node; abort merge
                 return null;
             }
-            encounteredValues.retainAll(nextValues);
-            if (encounteredValues.isEmpty()) {
+            if (encounteredValues.size() > 1) {
+                encounteredValues.retainAll(nextValues);
+                if (encounteredValues.isEmpty()) {
+                    // invalid merge result: no valid value remained; abort merge
+                    return null;
+                }
+            } else if (!nextValues.contains(encounteredValues.get(0))) {
                 // invalid merge result: no valid value remained; abort merge
                 return null;
             }
diff --git a/jsonschema-generator/src/test/java/com/github/victools/jsonschema/generator/SchemaGeneratorAllOfCleanUpTest.java b/jsonschema-generator/src/test/java/com/github/victools/jsonschema/generator/SchemaGeneratorAllOfCleanUpTest.java
index 96e11daf..1cb3d4a0 100644
--- a/jsonschema-generator/src/test/java/com/github/victools/jsonschema/generator/SchemaGeneratorAllOfCleanUpTest.java
+++ b/jsonschema-generator/src/test/java/com/github/victools/jsonschema/generator/SchemaGeneratorAllOfCleanUpTest.java
@@ -52,8 +52,23 @@ static Stream<Arguments> parametersForTestAllOfCleanUp() {
                                 + "\"allOf\": [{ \"title\":\"same in all three\" }, { \"title\":\"same in all three\" }] }",
                         "{ \"type\": \"object\", \"title\":\"same in all three\" }"),
                     Arguments.of(schemaVersion,
-                        "{ \"type\": \"object\",\"allOf\": [{ \"title\":\"from allOf[0]\" }, { \"description\":\"from allOf[1]\" }] }",
-                        "{ \"type\": \"object\", \"title\":\"from allOf[0]\", \"description\":\"from allOf[1]\" }")
+                        "{ \"type\": \"object\", \"allOf\": [{ \"title\":\"from allOf[0]\" }, { \"description\":\"from allOf[1]\" }] }",
+                        "{ \"type\": \"object\", \"title\":\"from allOf[0]\", \"description\":\"from allOf[1]\" }"),
+                    Arguments.of(schemaVersion,
+                        "{ \"type\": \"object\", \"allOf\": [{ \"type\": [\"object\",\"null\"] }] }",
+                        "{ \"type\": \"object\" }"),
+                    Arguments.of(schemaVersion,
+                        "{ \"type\": [\"object\",\"null\"], \"allOf\": [{ \"type\": \"object\" }] }",
+                        "{ \"type\": \"object\" }"),
+                    Arguments.of(schemaVersion,
+                        "{ \"type\": \"object\", \"allOf\": [{ \"type\": \"null\" }] }",
+                        "{ \"type\": \"object\", \"allOf\": [{ \"type\": \"null\" }] }"),
+                    Arguments.of(schemaVersion,
+                        "{ \"type\": \"object\", \"allOf\": [{ \"type\": [\"string\",\"null\"] }] }",
+                        "{ \"type\": \"object\", \"allOf\": [{ \"type\": [\"string\",\"null\"] }] }"),
+                    Arguments.of(schemaVersion,
+                        "{ \"type\": [\"object\",\"null\"], \"allOf\": [{ \"type\": \"string\" }] }",
+                        "{ \"type\": [\"object\",\"null\"], \"allOf\": [{ \"type\": \"string\" }] }")
                 ))
                 .collect(Collectors.toList());