diff --git a/src/gui/opengl/qopenglextensions_p.h b/src/gui/opengl/qopenglextensions_p.h
index aa2f784d86..ff5d79566c 100644
--- a/src/gui/opengl/qopenglextensions_p.h
+++ b/src/gui/opengl/qopenglextensions_p.h
@@ -135,6 +135,8 @@ public:
 
     QOpenGLES3Helper *gles3Helper();
 
+    void flushShared();
+
 private:
     static bool isInitialized(const QOpenGLFunctionsPrivate *d) { return d != 0; }
 };
@@ -158,6 +160,9 @@ public:
                                           GLsizei width, GLsizei height);
     void (QOPENGLF_APIENTRYP GetBufferSubData)(GLenum target, qopengl_GLintptr offset, qopengl_GLsizeiptr size, GLvoid *data);
     void (QOPENGLF_APIENTRYP DiscardFramebuffer)(GLenum target, GLsizei numAttachments, const GLenum *attachments);
+
+    bool flushVendorChecked;
+    bool flushIsSufficientToSyncContexts;
 };
 
 inline GLvoid *QOpenGLExtensions::glMapBuffer(GLenum target, GLenum access)
diff --git a/src/gui/opengl/qopenglfunctions.cpp b/src/gui/opengl/qopenglfunctions.cpp
index 587995515d..c60532b90b 100644
--- a/src/gui/opengl/qopenglfunctions.cpp
+++ b/src/gui/opengl/qopenglfunctions.cpp
@@ -3538,7 +3538,8 @@ QOpenGLFunctionsPrivate::QOpenGLFunctionsPrivate(QOpenGLContext *)
 }
 
 QOpenGLExtensionsPrivate::QOpenGLExtensionsPrivate(QOpenGLContext *ctx)
-    : QOpenGLFunctionsPrivate(ctx)
+    : QOpenGLFunctionsPrivate(ctx),
+      flushVendorChecked(false)
 {
     MapBuffer = qopenglfResolveMapBuffer;
     MapBufferRange = qopenglfResolveMapBufferRange;
@@ -3554,4 +3555,33 @@ QOpenGLES3Helper *QOpenGLExtensions::gles3Helper()
     return qgles3Helper();
 }
 
+void QOpenGLExtensions::flushShared()
+{
+    Q_D(QOpenGLExtensions);
+
+    if (!d->flushVendorChecked) {
+        d->flushVendorChecked = true;
+        // It is not quite clear if glFlush() is sufficient to synchronize access to
+        // resources between sharing contexts in the same thread. On most platforms this
+        // is enough (e.g. iOS explicitly documents it), while certain drivers only work
+        // properly when doing glFinish().
+        d->flushIsSufficientToSyncContexts = false; // default to false, not guaranteed by the spec
+        const char *vendor = (const char *) glGetString(GL_VENDOR);
+        if (vendor) {
+            static const char *flushEnough[] = { "Apple", "ATI", "Intel", "NVIDIA" };
+            for (size_t i = 0; i < sizeof(flushEnough) / sizeof(const char *); ++i) {
+                if (strstr(vendor, flushEnough[i])) {
+                    d->flushIsSufficientToSyncContexts = true;
+                    break;
+                }
+            }
+        }
+    }
+
+    if (d->flushIsSufficientToSyncContexts)
+        glFlush();
+    else
+        glFinish();
+}
+
 QT_END_NAMESPACE
diff --git a/src/widgets/kernel/qopenglwidget.cpp b/src/widgets/kernel/qopenglwidget.cpp
index 3b33894627..8faa9f8681 100644
--- a/src/widgets/kernel/qopenglwidget.cpp
+++ b/src/widgets/kernel/qopenglwidget.cpp
@@ -691,7 +691,7 @@ void QOpenGLWidgetPrivate::beginCompose()
     if (flushPending) {
         flushPending = false;
         q->makeCurrent();
-        context->functions()->glFlush();
+        static_cast<QOpenGLExtensions *>(context->functions())->flushShared();
     }
     hasBeenComposed = true;
     emit q->aboutToCompose();
@@ -768,7 +768,7 @@ void QOpenGLWidgetPrivate::resolveSamples()
         q->makeCurrent();
         QRect rect(QPoint(0, 0), fbo->size());
         QOpenGLFramebufferObject::blitFramebuffer(resolvedFbo, rect, fbo, rect);
-        QOpenGLContext::currentContext()->functions()->glFlush();
+        flushPending = true;
     }
 }
 
@@ -779,7 +779,7 @@ void QOpenGLWidgetPrivate::invokeUserPaint()
 
     f->glViewport(0, 0, q->width() * q->devicePixelRatio(), q->height() * q->devicePixelRatio());
     q->paintGL();
-    f->glFlush();
+    flushPending = true;
 }
 
 void QOpenGLWidgetPrivate::render()