diff --git a/src/BuiltInTools/dotnet-watch/HotReloadDotNetWatcher.cs b/src/BuiltInTools/dotnet-watch/HotReloadDotNetWatcher.cs
index 99f1122c9908..1f21e44a87f0 100644
--- a/src/BuiltInTools/dotnet-watch/HotReloadDotNetWatcher.cs
+++ b/src/BuiltInTools/dotnet-watch/HotReloadDotNetWatcher.cs
@@ -307,8 +307,8 @@ private static void ConfigureExecutable(DotNetWatchContext context, ProcessSpec
             }
 
             var rootVariableName = EnvironmentVariableNames.TryGetDotNetRootVariableName(
-                project.RuntimeIdentifier,
-                project.DefaultAppHostRuntimeIdentifier,
+                project.RuntimeIdentifier ?? "",
+                project.DefaultAppHostRuntimeIdentifier ?? "",
                 project.TargetFrameworkVersion);
 
             if (rootVariableName != null && string.IsNullOrEmpty(Environment.GetEnvironmentVariable(rootVariableName)))