diff --git a/packages/xod-client-electron/src/debugger/middleware.js b/packages/xod-client-electron/src/debugger/middleware.js
index 9af944be..0beefa19 100644
--- a/packages/xod-client-electron/src/debugger/middleware.js
+++ b/packages/xod-client-electron/src/debugger/middleware.js
@@ -1,10 +1,7 @@
 import client from 'xod-client';
 import { ipcRenderer } from 'electron';
 import { sendStopDebuggerSession } from './ipcActions';
-import {
-  DEBUG_SESSION_STOPPED_ON_CHANGE,
-  DEBUG_SESSION_STOPPED_ON_TAB_CLOSE,
-} from '../shared/messages';
+import { DEBUG_SESSION_STOPPED_ON_TAB_CLOSE } from '../shared/messages';
 
 export default store => next => action => {
   const state = store.getState();
@@ -16,8 +13,7 @@ export default store => next => action => {
 
   // Stop debug session if something changed in the Project
   if (isDebugSession && prevProject !== newProject) {
-    sendStopDebuggerSession(ipcRenderer);
-    store.dispatch(client.addError(DEBUG_SESSION_STOPPED_ON_CHANGE));
+    store.dispatch(client.markDebugSessionOutdated());
   }
 
   // Stop debug session if Debugger tab is closed
diff --git a/packages/xod-client-electron/src/shared/messages.js b/packages/xod-client-electron/src/shared/messages.js
index 4d590e0d..8f480855 100644
--- a/packages/xod-client-electron/src/shared/messages.js
+++ b/packages/xod-client-electron/src/shared/messages.js
@@ -20,11 +20,6 @@ export const SAVE_ALL_SUCCEED = {
   title: 'Saved successfully!',
 };
 
-export const DEBUG_SESSION_STOPPED_ON_CHANGE = {
-  title: 'Debug session stopped',
-  note: 'Your project has been changed.',
-  persistent: false,
-};
 export const DEBUG_SESSION_STOPPED_ON_TAB_CLOSE = {
   title: 'Debug session stopped',
   note: 'You closed the debugger tab.',
diff --git a/packages/xod-client/src/core/styles/components/Debugger.scss b/packages/xod-client/src/core/styles/components/Debugger.scss
index ce0fa9fb..b320d4ce 100644
--- a/packages/xod-client/src/core/styles/components/Debugger.scss
+++ b/packages/xod-client/src/core/styles/components/Debugger.scss
@@ -7,6 +7,17 @@
   }
 }
 
+.debugging-outdated {
+  color: $apricot-light;
+  font-family: $font-family-normal;
+  font-size: $font-size-m;
+  padding: 12px;
+
+  span {
+    margin-left: .25em;
+  }
+}
+
 .Debugger {
   bottom: 0;
   height: 220px;
diff --git a/packages/xod-client/src/debugger/actionTypes.js b/packages/xod-client/src/debugger/actionTypes.js
index f2358ad6..5863ae15 100644
--- a/packages/xod-client/src/debugger/actionTypes.js
+++ b/packages/xod-client/src/debugger/actionTypes.js
@@ -9,3 +9,5 @@ export const DEBUG_SESSION_STARTED = 'DEBUG_SESSION_STARTED';
 export const DEBUG_SESSION_STOPPED = 'DEBUG_SESSION_STOPPED';
 
 export const DEBUG_DRILL_DOWN = 'DEBUG_DRILL_DOWN';
+
+export const MARK_DEBUG_SESSION_OUTDATED = 'MARK_DEBUG_SESSION_OUTDATED';
diff --git a/packages/xod-client/src/debugger/actions.js b/packages/xod-client/src/debugger/actions.js
index bc86c8ca..9ca75901 100644
--- a/packages/xod-client/src/debugger/actions.js
+++ b/packages/xod-client/src/debugger/actions.js
@@ -40,3 +40,7 @@ export const drillDown = (patchPath, nodeId) => ({
     nodeId,
   },
 });
+
+export const markDebugSessionOutdated = () => ({
+  type: AT.MARK_DEBUG_SESSION_OUTDATED,
+});
diff --git a/packages/xod-client/src/debugger/reducer.js b/packages/xod-client/src/debugger/reducer.js
index da2449b2..8f9c3fca 100644
--- a/packages/xod-client/src/debugger/reducer.js
+++ b/packages/xod-client/src/debugger/reducer.js
@@ -8,6 +8,7 @@ import {
   DEBUGGER_LOG_CLEAR,
   DEBUG_SESSION_STARTED,
   DEBUG_SESSION_STOPPED,
+  MARK_DEBUG_SESSION_OUTDATED,
 } from './actionTypes';
 
 import { UPLOAD_STATUS, UPLOAD_MSG_TYPE } from './constants';
@@ -137,6 +138,7 @@ export default (state = initialState, action) => {
         addMessageToLog(action.payload.message),
         R.assoc('nodeIdsMap', invertMap(action.payload.nodeIdsMap)),
         R.assoc('isRunning', true),
+        R.assoc('isOutdated', false),
         showDebuggerPane
       )(state);
     case DEBUG_SESSION_STOPPED:
@@ -146,6 +148,8 @@ export default (state = initialState, action) => {
         R.assoc('nodeIdsMap', {}),
         R.assoc('isRunning', false)
       )(state);
+    case MARK_DEBUG_SESSION_OUTDATED:
+      return R.assoc('isOutdated', true, state);
     default:
       return state;
   }
diff --git a/packages/xod-client/src/debugger/selectors.js b/packages/xod-client/src/debugger/selectors.js
index ed9a0e2f..af34db5b 100644
--- a/packages/xod-client/src/debugger/selectors.js
+++ b/packages/xod-client/src/debugger/selectors.js
@@ -18,6 +18,11 @@ export const isDebuggerVisible = R.compose(
   getDebuggerState
 );
 
+export const isDebugSessionOutdated = R.compose(
+  R.prop('isOutdated'),
+  getDebuggerState
+);
+
 export const getLog = R.compose(R.prop('log'), getDebuggerState);
 
 export const getUploadLog = R.compose(R.prop('uploadLog'), getDebuggerState);
diff --git a/packages/xod-client/src/debugger/state.js b/packages/xod-client/src/debugger/state.js
index 3e7a7806..967bafac 100644
--- a/packages/xod-client/src/debugger/state.js
+++ b/packages/xod-client/src/debugger/state.js
@@ -4,6 +4,7 @@ import { INTRODUCTION } from './messages';
 export default {
   isVisible: false,
   isRunning: false,
+  isOutdated: false,
   log: [],
   uploadLog: [createSystemMessage(INTRODUCTION)],
   nodeIdsMap: {},
diff --git a/packages/xod-client/src/editor/containers/Editor.jsx b/packages/xod-client/src/editor/containers/Editor.jsx
index 9707d97f..baf1e733 100644
--- a/packages/xod-client/src/editor/containers/Editor.jsx
+++ b/packages/xod-client/src/editor/containers/Editor.jsx
@@ -43,6 +43,7 @@ import SnackBar from '../../messages/containers/SnackBar';
 import Helpbox from './Helpbox';
 
 import Tooltip from '../../tooltip/components/Tooltip';
+import TooltipHOC from '../../tooltip/components/TooltipHOC';
 
 import Tabs from './Tabs';
 import DragLayer from './DragLayer';
@@ -225,11 +226,37 @@ class Editor extends React.Component {
       />
     ) : null;
 
+    const renderProgramChangedWarning = () =>
+      this.props.isDebugSessionOutdated ? (
+        <TooltipHOC
+          content={
+            <div>
+              The program on screen is newer than the program running on the
+              board.<br />
+              Watches and overall behavior can be incorrect. Stop debugging and
+              upload again to synchronize.
+            </div>
+          }
+          render={(onMouseOver, onMouseMove, onMouseLeave) => (
+            <div
+              className="debugging-outdated"
+              onMouseOver={onMouseOver}
+              onMouseMove={onMouseMove}
+              onMouseLeave={onMouseLeave}
+            >
+              Program changed
+              <Icon name="question-circle" />
+            </div>
+          )}
+        />
+      ) : null;
+
     const debuggerBreadcrumbs = foldMaybe(
       null,
       tab =>
         tab.id === DEBUGGER_TAB_ID && this.props.isDebugSessionRunning ? (
           <Breadcrumbs>
+            {renderProgramChangedWarning()}
             <button
               className="debug-session-stop-button Button Button--light"
               onClick={this.props.stopDebuggerSession}
@@ -286,6 +313,7 @@ Editor.propTypes = {
   patchesIndex: PropTypes.object,
   isHelpboxVisible: PropTypes.bool,
   isDebugSessionRunning: PropTypes.bool,
+  isDebugSessionOutdated: PropTypes.bool,
   suggesterIsVisible: PropTypes.bool,
   suggesterPlacePosition: PropTypes.object,
   isLibSuggesterVisible: PropTypes.bool,
@@ -329,6 +357,7 @@ const mapStateToProps = R.applySpec({
   isLibSuggesterVisible: EditorSelectors.isLibSuggesterVisible,
   isHelpboxVisible: EditorSelectors.isHelpboxVisible,
   isDebugSessionRunning: DebuggerSelectors.isDebugSession,
+  isDebugSessionOutdated: DebuggerSelectors.isDebugSessionOutdated,
   defaultNodePosition: EditorSelectors.getDefaultNodePlacePosition,
 });