diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/HaskellHttpClientCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/HaskellHttpClientCodegen.java
index fbbfae50a3bf..a78e9a703cae 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/HaskellHttpClientCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/HaskellHttpClientCodegen.java
@@ -1182,12 +1182,19 @@ private static boolean isMultipartOperation(List<Map<String, String>> consumes)
 
     @Override
     public String toVarName(String name) {
+        if (nameMapping.containsKey(name)) {
+            return nameMapping.get(name);
+        }
+
         return toVarName("", name);
     }
 
     public String toVarName(String prefix, String name) {
         boolean hasPrefix = !StringUtils.isBlank(prefix);
         name = underscore(sanitizeName(name.replaceAll("-", "_")));
+        if (name.equals("_")) {
+            name = "underscore";
+        }
         name = camelize(name, hasPrefix ? UPPERCASE_FIRST_CHAR : LOWERCASE_FIRST_LETTER);
 
         if (hasPrefix) {
@@ -1203,6 +1210,10 @@ public String toVarName(String prefix, String name) {
 
     @Override
     public String toParamName(String name) {
+        if (parameterNameMapping.containsKey(name)) {
+            return parameterNameMapping.get(name);
+        }
+
         return toVarName(name);
     }
 
diff --git a/modules/openapi-generator/src/main/resources/haskell-http-client/Core.mustache b/modules/openapi-generator/src/main/resources/haskell-http-client/Core.mustache
index e910264bdd0a..3ed2df43812b 100644
--- a/modules/openapi-generator/src/main/resources/haskell-http-client/Core.mustache
+++ b/modules/openapi-generator/src/main/resources/haskell-http-client/Core.mustache
@@ -14,6 +14,7 @@ Module : {{baseModule}}.Core
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TupleSections #-}
 {-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE TypeOperators #-}
 {-# LANGUAGE CPP #-}
 {-# OPTIONS_GHC -fno-warn-name-shadowing -fno-warn-unused-binds -fno-warn-unused-imports #-}
 
diff --git a/samples/client/petstore/haskell-http-client/lib/OpenAPIPetstore/Core.hs b/samples/client/petstore/haskell-http-client/lib/OpenAPIPetstore/Core.hs
index 9062b81abfcf..b94edcc77570 100644
--- a/samples/client/petstore/haskell-http-client/lib/OpenAPIPetstore/Core.hs
+++ b/samples/client/petstore/haskell-http-client/lib/OpenAPIPetstore/Core.hs
@@ -23,6 +23,7 @@ Module : OpenAPIPetstore.Core
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TupleSections #-}
 {-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE TypeOperators #-}
 {-# LANGUAGE CPP #-}
 {-# OPTIONS_GHC -fno-warn-name-shadowing -fno-warn-unused-binds -fno-warn-unused-imports #-}