diff --git a/src/Microsoft.AspNetCore.ResponseCaching/ResponseCacheMiddleware.cs b/src/Microsoft.AspNetCore.ResponseCaching/ResponseCacheMiddleware.cs
index b57bea561b..4b0889fc5d 100644
--- a/src/Microsoft.AspNetCore.ResponseCaching/ResponseCacheMiddleware.cs
+++ b/src/Microsoft.AspNetCore.ResponseCaching/ResponseCacheMiddleware.cs
@@ -355,7 +355,7 @@ namespace Microsoft.AspNetCore.ResponseCaching
                     }
                 }
             }
-            else if ((cachedResponseHeaders.LastModified ?? cachedResponseHeaders.Date) <= context.TypedRequestHeaders.IfUnmodifiedSince)
+            else if (context.TypedRequestHeaders.IfUnmodifiedSince != null && (cachedResponseHeaders.LastModified ?? cachedResponseHeaders.Date) <= context.TypedRequestHeaders.IfUnmodifiedSince)
             {
                 return true;
             }