diff --git a/src/vs/workbench/api/common/extHostTerminalService.ts b/src/vs/workbench/api/common/extHostTerminalService.ts
index 94b1782e588..b26797bdef4 100644
--- a/src/vs/workbench/api/common/extHostTerminalService.ts
+++ b/src/vs/workbench/api/common/extHostTerminalService.ts
@@ -288,8 +288,8 @@ export abstract class BaseExtHostTerminalService implements IExtHostTerminalServ
 	protected _activeTerminal: ExtHostTerminal | undefined;
 	protected _terminals: ExtHostTerminal[] = [];
 	protected _terminalProcesses: { [id: number]: ITerminalChildProcess } = {};
-	protected _initialDimensions: { [id: number]: ITerminalDimensionsDto } = {};
-	protected _startedExtensionTerminal: { [id: number]: boolean } = {};
+	protected _initialDimensions: { [id: number]: ITerminalDimensionsDto | undefined } = {};
+	protected _extensionTerminalAwaitingStart: { [id: number]: boolean | undefined } = {};
 	protected _getTerminalPromises: { [id: number]: Promise<ExtHostTerminal> } = {};
 
 	public get activeTerminal(): ExtHostTerminal | undefined { return this._activeTerminal; }
@@ -465,13 +465,12 @@ export abstract class BaseExtHostTerminalService implements IExtHostTerminalServ
 		}
 		await openPromise;
 
-		this._startedExtensionTerminal[id] = true;
 		if (this._terminalProcesses[id]) {
 			(this._terminalProcesses[id] as ExtHostPseudoterminal).startSendingEvents(initialDimensions);
 		} else {
-			if (initialDimensions) {
-				this._initialDimensions[id] = initialDimensions;
-			}
+			// Defer startSendingEvents call to when _setupExtHostProcessListeners is called
+			this._extensionTerminalAwaitingStart[id] = true;
+			this._initialDimensions[id] = initialDimensions;
 		}
 
 	}
@@ -489,7 +488,7 @@ export abstract class BaseExtHostTerminalService implements IExtHostTerminalServ
 		}
 		this._terminalProcesses[id] = p;
 
-		if (p instanceof ExtHostPseudoterminal && this._startedExtensionTerminal[id]) {
+		if (this._extensionTerminalAwaitingStart[id] && p instanceof ExtHostPseudoterminal) {
 			p.startSendingEvents(this._initialDimensions[id]);
 			delete this._initialDimensions[id];
 		}
@@ -531,7 +530,7 @@ export abstract class BaseExtHostTerminalService implements IExtHostTerminalServ
 
 		// Remove process reference
 		delete this._terminalProcesses[id];
-		delete this._startedExtensionTerminal[id];
+		delete this._extensionTerminalAwaitingStart[id];
 
 		// Send exit event to main side
 		this._proxy.$sendProcessExit(id, exitCode);