diff --git a/src/BuiltInTools/dotnet-watch/HotReloadDotNetWatcher.cs b/src/BuiltInTools/dotnet-watch/HotReloadDotNetWatcher.cs
index f2cf300fafbd..f33d6a1647b8 100644
--- a/src/BuiltInTools/dotnet-watch/HotReloadDotNetWatcher.cs
+++ b/src/BuiltInTools/dotnet-watch/HotReloadDotNetWatcher.cs
@@ -309,8 +309,8 @@ private void ConfigureExecutable(DotNetWatchContext context, ProcessSpec process
             }
 
             var rootVariableName = EnvironmentVariableNames.TryGetDotNetRootVariableName(
-                project.RuntimeIdentifier,
-                project.DefaultAppHostRuntimeIdentifier,
+                project.RuntimeIdentifier ?? "",
+                project.DefaultAppHostRuntimeIdentifier ?? "",
                 project.TargetFrameworkVersion);
 
             if (rootVariableName != null && string.IsNullOrEmpty(Environment.GetEnvironmentVariable(rootVariableName)))