diff --git a/backend/LexBoxApi/GraphQL/ProjectMutations.cs b/backend/LexBoxApi/GraphQL/ProjectMutations.cs
index c8370d960..b682e5703 100644
--- a/backend/LexBoxApi/GraphQL/ProjectMutations.cs
+++ b/backend/LexBoxApi/GraphQL/ProjectMutations.cs
@@ -406,6 +406,7 @@ public async Task<IQueryable<Project>> SoftDeleteProject(
         await dbContext.SaveChangesAsync();
         await hgService.SoftDeleteRepo(projectCode, timestamp);
         projectService.InvalidateProjectConfidentialityCache(projectId);
+        projectService.InvalidateProjectCodeCache(projectCode);
         await transaction.CommitAsync();
 
         return dbContext.Projects.Where(p => p.Id == projectId);
diff --git a/backend/LexBoxApi/Services/ProjectService.cs b/backend/LexBoxApi/Services/ProjectService.cs
index f32457958..21ec60f14 100644
--- a/backend/LexBoxApi/Services/ProjectService.cs
+++ b/backend/LexBoxApi/Services/ProjectService.cs
@@ -96,6 +96,12 @@ public async ValueTask<Guid> LookupProjectId(string projectCode)
         return projectId;
     }
 
+    public void InvalidateProjectCodeCache(string projectCode)
+    {
+        try { memoryCache.Remove($"ProjectIdForCode:{projectCode}"); }
+        catch (Exception) { }; // Never allow this to throw
+    }
+
     public async Task<BackupExecutor?> BackupProject(string code)
     {
         var exists = await dbContext.Projects.Where(p => p.Code == code)