diff --git a/Refit.Tests/RequestBuilder.cs b/Refit.Tests/RequestBuilder.cs
index cd84c657d..a61680d2f 100644
--- a/Refit.Tests/RequestBuilder.cs
+++ b/Refit.Tests/RequestBuilder.cs
@@ -250,6 +250,9 @@ public interface IRestMethodInfoTests
 
         [Get("/api/{id}")]
         Task IEnumerableThrowingError([Query(CollectionFormat.Multi)] IEnumerable<string> values);
+        
+        [Get("/foo")]
+        List<string> InvalidGenericReturnType();
     }
 
     public enum TestEnum { A, B, C }
@@ -1146,6 +1149,14 @@ public void ParameterMappingWithHeaderQueryParamAndQueryArrayParam()
             Assert.Single(fixture.HeaderParameterMap);
             Assert.Single(fixture.PropertyParameterMap);
         }
+        
+        [Fact]
+        public void GenericReturnTypeIsNotTaskOrObservableShouldThrow()
+        {
+            var input = typeof(IRestMethodInfoTests);
+            Assert.Throws<ArgumentException>(() => new RestMethodInfo(input,
+                input.GetMethods().First(x => x.Name == nameof(IRestMethodInfoTests.InvalidGenericReturnType))));
+        }
     }
 
     [Headers("User-Agent: RefitTestClient", "Api-Version: 1")]
diff --git a/Refit/RestMethodInfo.cs b/Refit/RestMethodInfo.cs
index 760c790bd..04ec347a8 100644
--- a/Refit/RestMethodInfo.cs
+++ b/Refit/RestMethodInfo.cs
@@ -463,8 +463,9 @@ static Dictionary<int, string> BuildHeaderParameterMap(List<ParameterInfo> param
         void DetermineReturnTypeInfo(MethodInfo methodInfo)
         {
             var returnType = methodInfo.ReturnType;
-            if (returnType.IsGenericType && (methodInfo.ReturnType.GetGenericTypeDefinition() != typeof(Task<>)
-                                             || methodInfo.ReturnType.GetGenericTypeDefinition() != typeof(IObservable<>)))
+            if (returnType.IsGenericType && (methodInfo.ReturnType.GetGenericTypeDefinition() == typeof(Task<>)
+                                             || methodInfo.ReturnType.GetGenericTypeDefinition() == typeof(ValueTask<>)
+                                             || methodInfo.ReturnType.GetGenericTypeDefinition() == typeof(IObservable<>)))
             {
                 ReturnType = returnType;
                 ReturnResultType = returnType.GetGenericArguments()[0];
@@ -488,7 +489,7 @@ void DetermineReturnTypeInfo(MethodInfo methodInfo)
                 DeserializedResultType = typeof(void);
             }
             else
-                throw new ArgumentException($"Method \"{methodInfo.Name}\" is invalid. All REST Methods must return either Task<T> or IObservable<T>");
+                throw new ArgumentException($"Method \"{methodInfo.Name}\" is invalid. All REST Methods must return either Task<T> or ValueTask<T> or IObservable<T>");
         }
 
         void DetermineIfResponseMustBeDisposed()