diff --git a/src/vs/workbench/contrib/debug/browser/debugService.ts b/src/vs/workbench/contrib/debug/browser/debugService.ts
index 0cf0497bec287..27bb4016459ce 100644
--- a/src/vs/workbench/contrib/debug/browser/debugService.ts
+++ b/src/vs/workbench/contrib/debug/browser/debugService.ts
@@ -6,7 +6,7 @@
 import * as aria from 'vs/base/browser/ui/aria/aria';
 import { Action, IAction } from 'vs/base/common/actions';
 import { distinct } from 'vs/base/common/arrays';
-import { raceTimeout, RunOnceScheduler } from 'vs/base/common/async';
+import { Queue, raceTimeout, RunOnceScheduler } from 'vs/base/common/async';
 import { CancellationTokenSource } from 'vs/base/common/cancellation';
 import { isErrorWithActions } from 'vs/base/common/errorMessage';
 import * as errors from 'vs/base/common/errors';
@@ -825,6 +825,7 @@ export class DebugService implements IDebugService {
 		return Promise.all(sessions.map(s => disconnect ? s.disconnect(undefined, suspend) : s.terminate()));
 	}
 
+	private variableSubstitutionQueue = new Queue<IConfig | undefined>();
 	private async substituteVariables(launch: ILaunch | undefined, config: IConfig): Promise<IConfig | undefined> {
 		const dbg = this.adapterManager.getDebugger(config.type);
 		if (dbg) {
@@ -838,7 +839,8 @@ export class DebugService implements IDebugService {
 				}
 			}
 			try {
-				return await dbg.substituteVariables(folder, config);
+				// Variable substitution can require user interaction, so only one of these should be running at a time.
+				return this.variableSubstitutionQueue.queue(() => dbg.substituteVariables(folder, config));
 			} catch (err) {
 				this.showError(err.message, undefined, !!launch?.getConfiguration(config.name));
 				return undefined;	// bail out