diff --git a/src/plugins/autotoolsprojectmanager/autotoolsmanager.cpp b/src/plugins/autotoolsprojectmanager/autotoolsmanager.cpp
index cdc806e3324..6e19e8516aa 100644
--- a/src/plugins/autotoolsprojectmanager/autotoolsmanager.cpp
+++ b/src/plugins/autotoolsprojectmanager/autotoolsmanager.cpp
@@ -29,27 +29,13 @@
 #include "autotoolsproject.h"
 #include "autotoolsprojectconstants.h"
 
-#include <coreplugin/icore.h>
-#include <coreplugin/idocument.h>
-#include <coreplugin/messagemanager.h>
-#include <projectexplorer/projectexplorerconstants.h>
-#include <projectexplorer/projectexplorer.h>
-#include <projectexplorer/session.h>
-
 using namespace ProjectExplorer;
 
 namespace AutotoolsProjectManager {
 namespace Internal {
 
-Project *AutotoolsManager::openProject(const QString &fileName, QString *errorString)
+Project *AutotoolsManager::openProject(const QString &fileName)
 {
-    if (!QFileInfo(fileName).isFile()) {
-        if (errorString)
-            *errorString = tr("Failed opening project \"%1\": Project is not a file")
-                .arg(fileName);
-        return 0;
-    }
-
     return new AutotoolsProject(fileName);
 }
 
diff --git a/src/plugins/autotoolsprojectmanager/autotoolsmanager.h b/src/plugins/autotoolsprojectmanager/autotoolsmanager.h
index dd857811ef6..500a2599ddc 100644
--- a/src/plugins/autotoolsprojectmanager/autotoolsmanager.h
+++ b/src/plugins/autotoolsprojectmanager/autotoolsmanager.h
@@ -44,7 +44,7 @@ class AutotoolsManager : public ProjectExplorer::IProjectManager
     Q_OBJECT
 
 public:
-    ProjectExplorer::Project *openProject(const QString &fileName, QString *errorString) override;
+    ProjectExplorer::Project *openProject(const QString &fileName) override;
     QString mimeType() const override;
 };
 
diff --git a/src/plugins/cmakeprojectmanager/cmakeprojectmanager.cpp b/src/plugins/cmakeprojectmanager/cmakeprojectmanager.cpp
index f7e4c22cd5e..46aaeb3347b 100644
--- a/src/plugins/cmakeprojectmanager/cmakeprojectmanager.cpp
+++ b/src/plugins/cmakeprojectmanager/cmakeprojectmanager.cpp
@@ -156,17 +156,9 @@ void CMakeManager::rescanProject(Project *project)
     cmakeProject->runCMake(); // by my experience: every rescan run requires cmake run too
 }
 
-Project *CMakeManager::openProject(const QString &fileName, QString *errorString)
+Project *CMakeManager::openProject(const QString &fileName)
 {
-    Utils::FileName file = Utils::FileName::fromString(fileName);
-    if (!file.toFileInfo().isFile()) {
-        if (errorString)
-            *errorString = tr("Failed opening project \"%1\": Project is not a file")
-                .arg(file.toUserOutput());
-        return 0;
-    }
-
-    return new CMakeProject(file);
+    return new CMakeProject(Utils::FileName::fromString(fileName));
 }
 
 QString CMakeManager::mimeType() const
diff --git a/src/plugins/cmakeprojectmanager/cmakeprojectmanager.h b/src/plugins/cmakeprojectmanager/cmakeprojectmanager.h
index cd8f414a814..e8e42059ae0 100644
--- a/src/plugins/cmakeprojectmanager/cmakeprojectmanager.h
+++ b/src/plugins/cmakeprojectmanager/cmakeprojectmanager.h
@@ -42,7 +42,7 @@ class CMakeManager : public ProjectExplorer::IProjectManager
 public:
     CMakeManager();
 
-    ProjectExplorer::Project *openProject(const QString &fileName, QString *errorString) override;
+    ProjectExplorer::Project *openProject(const QString &fileName) override;
     QString mimeType() const override;
 
 private:
diff --git a/src/plugins/genericprojectmanager/genericprojectmanager.cpp b/src/plugins/genericprojectmanager/genericprojectmanager.cpp
index 9e46f6c1ced..bde3d17c56b 100644
--- a/src/plugins/genericprojectmanager/genericprojectmanager.cpp
+++ b/src/plugins/genericprojectmanager/genericprojectmanager.cpp
@@ -27,13 +27,6 @@
 #include "genericprojectconstants.h"
 #include "genericproject.h"
 
-#include <coreplugin/icore.h>
-#include <projectexplorer/projectexplorer.h>
-#include <projectexplorer/projectexplorerconstants.h>
-#include <projectexplorer/session.h>
-
-#include <QDebug>
-
 namespace GenericProjectManager {
 namespace Internal {
 
@@ -42,15 +35,8 @@ QString Manager::mimeType() const
     return QLatin1String(Constants::GENERICMIMETYPE);
 }
 
-ProjectExplorer::Project *Manager::openProject(const QString &fileName, QString *errorString)
+ProjectExplorer::Project *Manager::openProject(const QString &fileName)
 {
-    if (!QFileInfo(fileName).isFile()) {
-        if (errorString)
-            *errorString = tr("Failed opening project \"%1\": Project is not a file.")
-                .arg(fileName);
-        return 0;
-    }
-
     return new GenericProject(fileName);
 }
 
diff --git a/src/plugins/genericprojectmanager/genericprojectmanager.h b/src/plugins/genericprojectmanager/genericprojectmanager.h
index 139739c827b..213de64644f 100644
--- a/src/plugins/genericprojectmanager/genericprojectmanager.h
+++ b/src/plugins/genericprojectmanager/genericprojectmanager.h
@@ -38,7 +38,7 @@ class Manager : public ProjectExplorer::IProjectManager
 
 public:
     virtual QString mimeType() const override;
-    virtual ProjectExplorer::Project *openProject(const QString &fileName, QString *errorString) override;
+    virtual ProjectExplorer::Project *openProject(const QString &fileName) override;
 
     void registerProject(GenericProject *project);
     void unregisterProject(GenericProject *project);
diff --git a/src/plugins/nim/project/nimprojectmanager.cpp b/src/plugins/nim/project/nimprojectmanager.cpp
index 3a529519164..3235b0f0dec 100644
--- a/src/plugins/nim/project/nimprojectmanager.cpp
+++ b/src/plugins/nim/project/nimprojectmanager.cpp
@@ -37,13 +37,8 @@ QString NimProjectManager::mimeType() const
     return QLatin1String(Constants::C_NIM_PROJECT_MIMETYPE);
 }
 
-Project *NimProjectManager::openProject(const QString &fileName, QString *errorString)
+Project *NimProjectManager::openProject(const QString &fileName)
 {
-    if (!QFileInfo(fileName).isFile()) {
-        *errorString = tr("Failed opening project \"%1\": Project is not a file.").arg(fileName);
-        return nullptr;
-    }
-
     return new NimProject(fileName);
 }
 
diff --git a/src/plugins/nim/project/nimprojectmanager.h b/src/plugins/nim/project/nimprojectmanager.h
index 81703d16fd2..a5336e465bc 100644
--- a/src/plugins/nim/project/nimprojectmanager.h
+++ b/src/plugins/nim/project/nimprojectmanager.h
@@ -36,7 +36,7 @@ class NimProjectManager : public ProjectExplorer::IProjectManager
 public:
     QString mimeType() const override;
 
-    ProjectExplorer::Project *openProject(const QString &fileName, QString *errorString) override;
+    ProjectExplorer::Project *openProject(const QString &fileName) override;
 };
 
 }
diff --git a/src/plugins/projectexplorer/iprojectmanager.h b/src/plugins/projectexplorer/iprojectmanager.h
index 7d25e9ba026..ff01c83a113 100644
--- a/src/plugins/projectexplorer/iprojectmanager.h
+++ b/src/plugins/projectexplorer/iprojectmanager.h
@@ -39,8 +39,8 @@ class PROJECTEXPLORER_EXPORT IProjectManager : public QObject
 
 public:
     virtual QString mimeType() const = 0;
-    // fileName is a canonical path!
-    virtual Project *openProject(const QString &fileName, QString *errorString) = 0;
+    // FileName is a canonical path of a checked-to-exist file.
+    virtual Project *openProject(const QString &fileName) = 0;
 };
 
 } // namespace ProjectExplorer
diff --git a/src/plugins/projectexplorer/jsonwizard/jsonkitspage.cpp b/src/plugins/projectexplorer/jsonwizard/jsonkitspage.cpp
index e9059a656a7..12e5d7556cd 100644
--- a/src/plugins/projectexplorer/jsonwizard/jsonkitspage.cpp
+++ b/src/plugins/projectexplorer/jsonwizard/jsonkitspage.cpp
@@ -109,7 +109,6 @@ void JsonKitsPage::setupProjectFiles(const JsonWizard::GeneratorFiles &files)
 
     foreach (const JsonWizard::GeneratorFile &f, files) {
         if (f.file.attributes() & GeneratedFile::OpenProjectAttribute) {
-            QString errorMessage;
             const QFileInfo fi(f.file.path());
             const QString path = fi.absoluteFilePath();
 
@@ -119,7 +118,7 @@ void JsonKitsPage::setupProjectFiles(const JsonWizard::GeneratorFiles &files)
                 continue;
 
             auto manager = Utils::findOrDefault(managerList, Utils::equal(&IProjectManager::mimeType, mt.name()));
-            project = manager ? manager->openProject(path, &errorMessage) : nullptr;
+            project = manager ? manager->openProject(path) : nullptr;
             if (project) {
                 if (setupProject(project))
                     project->saveSettings();
diff --git a/src/plugins/projectexplorer/projectexplorer.cpp b/src/plugins/projectexplorer/projectexplorer.cpp
index de3cef38551..9940afa0b35 100644
--- a/src/plugins/projectexplorer/projectexplorer.cpp
+++ b/src/plugins/projectexplorer/projectexplorer.cpp
@@ -1707,8 +1707,10 @@ ProjectExplorerPlugin::OpenProjectResult ProjectExplorerPlugin::openProjects(con
             foreach (IProjectManager *manager, projectManagers) {
                 if (mt.matchesName(manager->mimeType())) {
                     foundProjectManager = true;
-                    QString tmp;
-                    if (Project *pro = manager->openProject(filePath, &tmp)) {
+                    if (!QFileInfo(filePath).isFile()) {
+                         appendError(errorString,
+                            tr("Failed opening project \"%1\": Project is not a file").arg(fileName));
+                    } else if (Project *pro = manager->openProject(filePath)) {
                         pro->setProjectManager(manager);
                         QObject::connect(pro, &Project::parsingFinished, [pro]() {
                             emit SessionManager::instance()->projectFinishedParsing(pro);
@@ -1726,8 +1728,6 @@ ProjectExplorerPlugin::OpenProjectResult ProjectExplorerPlugin::openProjects(con
                             delete pro;
                         }
                     }
-                    if (!tmp.isEmpty())
-                        appendError(errorString, tmp);
                     break;
                 }
             }
diff --git a/src/plugins/pythoneditor/pythoneditorplugin.cpp b/src/plugins/pythoneditor/pythoneditorplugin.cpp
index d66eb705ded..543113f583e 100644
--- a/src/plugins/pythoneditor/pythoneditorplugin.cpp
+++ b/src/plugins/pythoneditor/pythoneditorplugin.cpp
@@ -94,7 +94,7 @@ class PythonProjectManager : public IProjectManager
     Q_OBJECT
 public:
     QString mimeType() const override { return QLatin1String(PythonMimeType); }
-    Project *openProject(const QString &fileName, QString *errorString) override;
+    Project *openProject(const QString &fileName) override;
 };
 
 class PythonProject : public Project
@@ -361,15 +361,8 @@ PythonRunConfigurationWidget::PythonRunConfigurationWidget(PythonRunConfiguratio
     setEnabled(runConfiguration->isEnabled());
 }
 
-Project *PythonProjectManager::openProject(const QString &fileName, QString *errorString)
+Project *PythonProjectManager::openProject(const QString &fileName)
 {
-    if (!QFileInfo(fileName).isFile()) {
-        if (errorString)
-            *errorString = tr("Failed opening project \"%1\": Project is not a file.")
-                .arg(fileName);
-        return 0;
-    }
-
     return new PythonProject(fileName);
 }
 
diff --git a/src/plugins/qbsprojectmanager/qbsprojectmanager.cpp b/src/plugins/qbsprojectmanager/qbsprojectmanager.cpp
index bc5f41711f9..0d2a489d697 100644
--- a/src/plugins/qbsprojectmanager/qbsprojectmanager.cpp
+++ b/src/plugins/qbsprojectmanager/qbsprojectmanager.cpp
@@ -105,15 +105,8 @@ QString QbsManager::mimeType() const
     return QLatin1String(QmlJSTools::Constants::QBS_MIMETYPE);
 }
 
-ProjectExplorer::Project *QbsManager::openProject(const QString &fileName, QString *errorString)
+ProjectExplorer::Project *QbsManager::openProject(const QString &fileName)
 {
-    if (!QFileInfo(fileName).isFile()) {
-        if (errorString)
-            *errorString = tr("Failed opening project \"%1\": Project is not a file.")
-                .arg(fileName);
-        return nullptr;
-    }
-
     return new QbsProject(fileName);
 }
 
diff --git a/src/plugins/qbsprojectmanager/qbsprojectmanager.h b/src/plugins/qbsprojectmanager/qbsprojectmanager.h
index ecade37059d..fa9af9cf2ca 100644
--- a/src/plugins/qbsprojectmanager/qbsprojectmanager.h
+++ b/src/plugins/qbsprojectmanager/qbsprojectmanager.h
@@ -60,7 +60,7 @@ public:
     ~QbsManager();
 
     QString mimeType() const override;
-    ProjectExplorer::Project *openProject(const QString &fileName, QString *errorString) override;
+    ProjectExplorer::Project *openProject(const QString &fileName) override;
 
     // QBS profiles management:
     QString profileForKit(const ProjectExplorer::Kit *k);
diff --git a/src/plugins/qmakeprojectmanager/qmakeprojectmanager.cpp b/src/plugins/qmakeprojectmanager/qmakeprojectmanager.cpp
index e2563f14224..8bf477cb43b 100644
--- a/src/plugins/qmakeprojectmanager/qmakeprojectmanager.cpp
+++ b/src/plugins/qmakeprojectmanager/qmakeprojectmanager.cpp
@@ -74,15 +74,8 @@ QString QmakeManager::mimeType() const
     return QLatin1String(QmakeProjectManager::Constants::PROFILE_MIMETYPE);
 }
 
-ProjectExplorer::Project *QmakeManager::openProject(const QString &fileName, QString *errorString)
+ProjectExplorer::Project *QmakeManager::openProject(const QString &fileName)
 {
-    if (!QFileInfo(fileName).isFile()) {
-        if (errorString)
-            *errorString = tr("Failed opening project \"%1\": Project is not a file")
-                .arg(fileName);
-        return 0;
-    }
-
     return new QmakeProject(this, fileName);
 }
 
diff --git a/src/plugins/qmakeprojectmanager/qmakeprojectmanager.h b/src/plugins/qmakeprojectmanager/qmakeprojectmanager.h
index a32cb665ef7..bf472002ef6 100644
--- a/src/plugins/qmakeprojectmanager/qmakeprojectmanager.h
+++ b/src/plugins/qmakeprojectmanager/qmakeprojectmanager.h
@@ -53,7 +53,7 @@ public:
     void notifyChanged(const Utils::FileName &name);
 
     QString mimeType() const override;
-    ProjectExplorer::Project *openProject(const QString &fileName, QString *errorString) override;
+    ProjectExplorer::Project *openProject(const QString &fileName) override;
 
     // Context information used in the slot implementations
     static ProjectExplorer::Node *contextNode();
diff --git a/src/plugins/qmlprojectmanager/qmlprojectmanager.cpp b/src/plugins/qmlprojectmanager/qmlprojectmanager.cpp
index 9af1acfcd08..b2669bf46b5 100644
--- a/src/plugins/qmlprojectmanager/qmlprojectmanager.cpp
+++ b/src/plugins/qmlprojectmanager/qmlprojectmanager.cpp
@@ -43,15 +43,8 @@ Manager::Manager()
 QString Manager::mimeType() const
 { return QLatin1String(Constants::QMLPROJECT_MIMETYPE); }
 
-ProjectExplorer::Project *Manager::openProject(const QString &fileName, QString *errorString)
+ProjectExplorer::Project *Manager::openProject(const QString &fileName)
 {
-    if (!QFileInfo(fileName).isFile()) {
-        if (errorString)
-            *errorString = tr("Failed opening project \"%1\": Project is not a file.")
-                .arg(fileName);
-        return 0;
-    }
-
     return new QmlProject(this, Utils::FileName::fromString(fileName));
 }
 
diff --git a/src/plugins/qmlprojectmanager/qmlprojectmanager.h b/src/plugins/qmlprojectmanager/qmlprojectmanager.h
index 0b0038fa6b2..0d49694a75c 100644
--- a/src/plugins/qmlprojectmanager/qmlprojectmanager.h
+++ b/src/plugins/qmlprojectmanager/qmlprojectmanager.h
@@ -39,7 +39,7 @@ public:
     Manager();
 
     QString mimeType() const override;
-    ProjectExplorer::Project *openProject(const QString &fileName, QString *errorString) override;
+    ProjectExplorer::Project *openProject(const QString &fileName) override;
 };
 
 } // namespace Internal