diff --git a/src/vs/workbench/contrib/debug/browser/debugService.ts b/src/vs/workbench/contrib/debug/browser/debugService.ts
index ca52621436044bfe588a8ae6fd8e7d6edfcecc5c..9a168614fcb5595451318719f39806e177865508 100644
--- a/src/vs/workbench/contrib/debug/browser/debugService.ts
+++ b/src/vs/workbench/contrib/debug/browser/debugService.ts
@@ -760,8 +760,9 @@ export class DebugService implements IDebugService {
 				const control = editor.getControl();
 				if (stackFrame && isCodeEditor(control) && control.hasModel()) {
 					const model = control.getModel();
-					if (stackFrame.range.startLineNumber <= model.getLineCount()) {
-						const lineContent = control.getModel().getLineContent(stackFrame.range.startLineNumber);
+					const lineNumber = stackFrame.range.startLineNumber;
+					if (lineNumber >= 1 && lineNumber <= model.getLineCount()) {
+						const lineContent = control.getModel().getLineContent(lineNumber);
 						aria.alert(nls.localize('debuggingPaused', "Debugging paused {0}, {1} {2} {3}", thread && thread.stoppedDetails ? `, reason ${thread.stoppedDetails.reason}` : '', stackFrame.source ? stackFrame.source.name : '', stackFrame.range.startLineNumber, lineContent));
 					}
 				}