diff --git a/Recurly.Tests/BaseClientTest.cs b/Recurly.Tests/BaseClientTest.cs
index 6b80ff0b..ca01cbef 100644
--- a/Recurly.Tests/BaseClientTest.cs
+++ b/Recurly.Tests/BaseClientTest.cs
@@ -138,10 +138,15 @@ public void WillThrowARecurlyErrorForUnknownErrors()
         [Fact]
         public void WillThrowAnApiErrorForUnknownErrorType()
         {
+            // Force RECURLY_STRICT_MODE for this test
+            Environment.SetEnvironmentVariable("RECURLY_STRICT_MODE", "TRUE");
+
             var client = MockClient.Build(UnknownTypeResponse());
             // Instead of disabling strict mode, test with ArgumentException as proxy
             var exception = Assert.Throws<System.ArgumentException>(() => client.GetResource("benjamin", "param1", new DateTime(2020, 01, 01)));
             Assert.Matches("no valid exception class", exception.Message);
+
+            Environment.SetEnvironmentVariable("RECURLY_STRICT_MODE", null);
         }
 
         [Fact]
diff --git a/Recurly/Utils.cs b/Recurly/Utils.cs
index dda939f8..2d0d0892 100644
--- a/Recurly/Utils.cs
+++ b/Recurly/Utils.cs
@@ -19,7 +19,7 @@ public static bool StrictMode
                     {
                         if (!strictMode.HasValue)
                         {
-                            strictMode = Environment.GetEnvironmentVariable("RECURLY_STRICT_MODE").ToUpper() == "TRUE";
+                            strictMode = Environment.GetEnvironmentVariable("RECURLY_STRICT_MODE")?.ToUpper() == "TRUE";
                         }
                     }
                 }