diff --git a/modules/openapi-generator/src/main/resources/csharp-refactor/ClientUtils.mustache b/modules/openapi-generator/src/main/resources/csharp-refactor/ClientUtils.mustache
index 73d368321f3..7b88f488135 100755
--- a/modules/openapi-generator/src/main/resources/csharp-refactor/ClientUtils.mustache
+++ b/modules/openapi-generator/src/main/resources/csharp-refactor/ClientUtils.mustache
@@ -204,7 +204,7 @@ namespace {{packageName}}.Client
 
             foreach (var contentType in contentTypes)
             {
-                if (IsJsonMime(contentType.ToLower()))
+                if (IsJsonMime(contentType))
                     return contentType;
             }
 
@@ -229,6 +229,11 @@ namespace {{packageName}}.Client
             return String.Join(",", accepts);
         }
 
+        /// <summary>
+        /// Provides a case-insensitive check that a provided content type is a known JSON-like content type.
+        /// </summary>
+        public static readonly Regex JsonRegex = new Regex("(?i)^(application/json|[^;/ \t]+/[^;/ \t]+[+]json)[ \t]*(;.*)?$");
+
         /// <summary>
         /// Check if the given MIME is a JSON MIME.
         /// JSON MIME examples:
@@ -241,8 +246,9 @@ namespace {{packageName}}.Client
         /// <returns>Returns True if MIME type is json.</returns>
         public static bool IsJsonMime(String mime)
         {
-            var jsonRegex = new Regex("(?i)^(application/json|[^;/ \t]+/[^;/ \t]+[+]json)[ \t]*(;.*)?$");
-            return mime != null && (jsonRegex.IsMatch(mime) || mime.Equals("application/json-patch+json"));
+            if (String.IsNullOrWhiteSpace(mime)) return false;
+
+            return JsonRegex.IsMatch(mime) || mime.Equals("application/json-patch+json");
         }
     }
 }
diff --git a/samples/client/petstore/csharp-refactor/OpenAPIClient/src/Org.OpenAPITools/Client/ClientUtils.cs b/samples/client/petstore/csharp-refactor/OpenAPIClient/src/Org.OpenAPITools/Client/ClientUtils.cs
index f56a9f185be..cbbe60300fd 100644
--- a/samples/client/petstore/csharp-refactor/OpenAPIClient/src/Org.OpenAPITools/Client/ClientUtils.cs
+++ b/samples/client/petstore/csharp-refactor/OpenAPIClient/src/Org.OpenAPITools/Client/ClientUtils.cs
@@ -208,7 +208,7 @@ namespace Org.OpenAPITools.Client
 
             foreach (var contentType in contentTypes)
             {
-                if (IsJsonMime(contentType.ToLower()))
+                if (IsJsonMime(contentType))
                     return contentType;
             }
 
@@ -233,6 +233,11 @@ namespace Org.OpenAPITools.Client
             return String.Join(",", accepts);
         }
 
+        /// <summary>
+        /// Provides a case-insensitive check that a provided content type is a known JSON-like content type.
+        /// </summary>
+        public static readonly Regex JsonRegex = new Regex("(?i)^(application/json|[^;/ \t]+/[^;/ \t]+[+]json)[ \t]*(;.*)?$");
+
         /// <summary>
         /// Check if the given MIME is a JSON MIME.
         /// JSON MIME examples:
@@ -245,8 +250,9 @@ namespace Org.OpenAPITools.Client
         /// <returns>Returns True if MIME type is json.</returns>
         public static bool IsJsonMime(String mime)
         {
-            var jsonRegex = new Regex("(?i)^(application/json|[^;/ \t]+/[^;/ \t]+[+]json)[ \t]*(;.*)?$");
-            return mime != null && (jsonRegex.IsMatch(mime) || mime.Equals("application/json-patch+json"));
+            if (String.IsNullOrWhiteSpace(mime)) return false;
+
+            return JsonRegex.IsMatch(mime) || mime.Equals("application/json-patch+json");
         }
     }
 }