diff --git a/src/main/antlr/To.g4 b/src/main/antlr/To.g4
index 96805b41..2feba67c 100644
--- a/src/main/antlr/To.g4
+++ b/src/main/antlr/To.g4
@@ -41,7 +41,6 @@ typeArgumentList
 typeArgument
   : type
   | '?'
-  | .*?
   ;
 
 
diff --git a/src/main/kotlin/io/openapiprocessor/core/model/datatypes/MappedDataType.kt b/src/main/kotlin/io/openapiprocessor/core/model/datatypes/MappedDataType.kt
index 6e1a2d5d..67fd9c3c 100644
--- a/src/main/kotlin/io/openapiprocessor/core/model/datatypes/MappedDataType.kt
+++ b/src/main/kotlin/io/openapiprocessor/core/model/datatypes/MappedDataType.kt
@@ -44,7 +44,7 @@ open class MappedDataType(
     }
 
     override fun getImports(): Set<String> {
-        return setOf("${getPackageName()}.$type") + genericTypes
+        return setOf("${getPackageName()}.$type") + genericTypes.filter { it != "?" }
     }
 
     private fun getGenericTypeNames(): List<String> {
diff --git a/src/main/kotlin/io/openapiprocessor/core/processor/mapping/v2/parser/ToExtractor.kt b/src/main/kotlin/io/openapiprocessor/core/processor/mapping/v2/parser/ToExtractor.kt
index fbdd72d0..3c5d01aa 100644
--- a/src/main/kotlin/io/openapiprocessor/core/processor/mapping/v2/parser/ToExtractor.kt
+++ b/src/main/kotlin/io/openapiprocessor/core/processor/mapping/v2/parser/ToExtractor.kt
@@ -35,9 +35,12 @@ class ToExtractor: ToBaseListener() {
         ctx.typeArguments ()
             ?.typeArgumentList ()
             ?.typeArgument ()
-            ?.filter { it.type() != null }
             ?.forEach {
-                typeArguments.add(it.type ().text)
+                if (it.text == "?") {
+                    typeArguments.add("?")
+                } else if (it.type() != null) {
+                    typeArguments.add(it.type ().text)
+                }
             }
     }
 
diff --git a/src/test/groovy/com/github/hauner/openapi/core/model/datatypes/MappedDataTypeSpec.groovy b/src/test/groovy/com/github/hauner/openapi/core/model/datatypes/MappedDataTypeSpec.groovy
index 57a2b4e5..599aa5e5 100644
--- a/src/test/groovy/com/github/hauner/openapi/core/model/datatypes/MappedDataTypeSpec.groovy
+++ b/src/test/groovy/com/github/hauner/openapi/core/model/datatypes/MappedDataTypeSpec.groovy
@@ -32,6 +32,7 @@ class MappedDataTypeSpec extends Specification {
         where:
         generics                                 | typeName
         []                                       | 'Foo'
+        ['?']                                    | 'Foo<?>'
         ['java.lang.String']                     | 'Foo<String>'
         ['java.lang.String', 'java.lang.String'] | 'Foo<String, String>'
     }
@@ -46,6 +47,7 @@ class MappedDataTypeSpec extends Specification {
         where:
         generics                                 | imports
         []                                       | ['model.Foo']
+        ['?']                                    | ['model.Foo']
         ['java.lang.String']                     | ['model.Foo', 'java.lang.String']
         ['java.lang.String', 'java.lang.String'] | ['model.Foo', 'java.lang.String']
     }
diff --git a/src/test/groovy/io/openapiprocessor/core/processor/mapping/v2/parser/ToParserSpec.groovy b/src/test/groovy/io/openapiprocessor/core/processor/mapping/v2/parser/ToParserSpec.groovy
index 9722b0dc..813773a6 100644
--- a/src/test/groovy/io/openapiprocessor/core/processor/mapping/v2/parser/ToParserSpec.groovy
+++ b/src/test/groovy/io/openapiprocessor/core/processor/mapping/v2/parser/ToParserSpec.groovy
@@ -35,7 +35,7 @@ class ToParserSpec extends Specification {
         'io.openapiprocessor.Foo'         | 'io.openapiprocessor.Foo' | []
         '  io . openapiprocessor .  Foo ' | 'io.openapiprocessor.Foo' | []
         'A<>'                             | 'A'                       | []
-        'A<?>'                            | 'A'                       | []
+        'A<?>'                            | 'A'                       | ['?']
         'A<b.B, c.C>'                     | 'A'                       | ['b.B', 'c.C']
         'A<B, C>'                         | 'A'                       | ['B', 'C']
     }