diff --git a/components/gitpod-protocol/src/protocol.ts b/components/gitpod-protocol/src/protocol.ts
index 498ee53bcca63d..7c3fec948138f6 100644
--- a/components/gitpod-protocol/src/protocol.ts
+++ b/components/gitpod-protocol/src/protocol.ts
@@ -1127,7 +1127,7 @@ export interface WithCommitHistory {
 
 export interface StartPrebuildContext extends WorkspaceContext, WithCommitHistory {
     actual: WorkspaceContext;
-    project?: Project;
+    project: Project;
     branch?: string;
 }
 
diff --git a/components/server/ee/src/prebuilds/prebuild-manager.ts b/components/server/ee/src/prebuilds/prebuild-manager.ts
index fe6c8e0b96c6f3..c3fb20b99fa5b5 100644
--- a/components/server/ee/src/prebuilds/prebuild-manager.ts
+++ b/components/server/ee/src/prebuilds/prebuild-manager.ts
@@ -128,6 +128,11 @@ export class PrebuildManager {
             if (user.blocked) {
                 throw new Error(`Blocked users cannot start prebuilds (${user.name})`);
             }
+            if (!project) {
+                throw new Error(
+                    `Running prebuilds without a project is no longer supported. Please add '${cloneURL}' as a project in a Gitpod team.`,
+                );
+            }
             const existingPB = await this.findNonFailedPrebuiltWorkspace({ span }, cloneURL, commitSHAIdentifier);
 
             // If the existing prebuild is failed, it will be retriggered in the afterwards