diff --git a/doc/changelog.dox b/doc/changelog.dox
index b7b98df1f..eaed80ba0 100644
--- a/doc/changelog.dox
+++ b/doc/changelog.dox
@@ -196,6 +196,13 @@ See also:
     now advertised as a @cpp "intel-windows-chatty-shader-compiler" @ce
     workaround, instead of being done silently. See @ref opengl-workarounds for
     more information.
+-   @ref Platform::WindowlessEglApplication "Platform::Windowless*Application"
+    instances no longer touch default framebuffer state in order to avoid
+    potential race conditions with a windowed context on another thread. This
+    is also exposed via a new @ref GL::Context::Configuration::Flag::Windowless
+    flag for integration with custom-created OpenGL contexts. See also
+    [mosra/magnum#493](https://github.com/mosra/magnum/pull/493) and
+    [mosra/magnum#494](https://github.com/mosra/magnum/pull/494).
 
 @subsubsection changelog-latest-changes-math Math library
 
diff --git a/src/Magnum/GL/Context.cpp b/src/Magnum/GL/Context.cpp
index 288a837b9..d1069ac8c 100644
--- a/src/Magnum/GL/Context.cpp
+++ b/src/Magnum/GL/Context.cpp
@@ -785,6 +785,10 @@ bool Context::tryCreate(const Configuration& configuration) {
     if(configuration.flags() & Configuration::Flag::GpuValidation)
         _configurationFlags |= Configuration::Flag::GpuValidation;
 
+    /* Same for windowless */
+    if(configuration.flags() & Configuration::Flag::Windowless)
+        _configurationFlags |= Configuration::Flag::Windowless;
+
     /* Driver workarounds get merged. Not using disableDriverWorkaround() here
        since the Configuration already contains the internal string views. */
     for(const Containers::StringView workaround: configuration.disabledWorkarounds())
@@ -974,9 +978,13 @@ bool Context::tryCreate(const Configuration& configuration) {
             if(!workaround.second) Debug(output) << "   " << workaround.first;
     }
 
-    /* Initialize functionality based on current OpenGL version and extensions */
     /** @todo Get rid of these */
-    DefaultFramebuffer::initializeContextBasedFunctionality(*this);
+    /* Initialize functionality based on current OpenGL version and extensions.
+       If we are on a windowless context don't touch the default framebuffer
+       to avoid potential race conditions with default framebuffer on another
+       thread. */
+    if(!(_configurationFlags & Configuration::Flag::Windowless))
+        DefaultFramebuffer::initializeContextBasedFunctionality(*this);
     Renderer::initializeContextBasedFunctionality();
 
     /* Enable GPU validation, if requested */
diff --git a/src/Magnum/GL/Context.h b/src/Magnum/GL/Context.h
index 9d38e146a..86a6763ed 100644
--- a/src/Magnum/GL/Context.h
+++ b/src/Magnum/GL/Context.h
@@ -70,6 +70,7 @@ namespace Implementation {
        Context before the Configuration class is defined, it has to be here */
     enum class ContextConfigurationFlag: UnsignedLong {
         /* Keeping the 32-bit range reserved for actual GL context flags */
+        Windowless = 1ull << 60,
         QuietLog = 1ull << 61,
         VerboseLog = 1ull << 62,
         GpuValidation = 1ull << 63
@@ -914,6 +915,19 @@ class MAGNUM_GL_EXPORT Context::Configuration {
             /* Docs only, keep in sync with
                Implementation::ContextConfigurationFlag please */
 
+            /**
+             * Treat the context as windowless, assume there's no default
+             * framebuffer and thus don't touch @ref defaultFramebuffer in any
+             * way. Useful for preventing race conditions when creating OpenGL
+             * contexts in background threads.
+             *
+             * This flag is implicitly enabled in all
+             * @ref Platform::WindowlessEglContext::Configuration "Platform::Windowless*Application::Configuration",
+             * and, conversely, not possible to enable in any
+             * @ref Platform::Sdl2Application::GLConfiguration::Flag "Platform::*Application::GLConfiguration".
+             */
+            Windowless = 1ull << 60,
+
             /**
              * Print only warnings and errors instead of the usual startup log
              * listing used extensions and workarounds. Ignored if
diff --git a/src/Magnum/GL/Framebuffer.cpp b/src/Magnum/GL/Framebuffer.cpp
index 135534bdf..e1edba78a 100644
--- a/src/Magnum/GL/Framebuffer.cpp
+++ b/src/Magnum/GL/Framebuffer.cpp
@@ -120,18 +120,23 @@ Framebuffer::~Framebuffer() {
     if(!_id || !(_flags & ObjectFlag::DeleteOnDestruction)) return;
 
     /* If bound, remove itself from state */
-    Implementation::FramebufferState& state = Context::current().state().framebuffer;
+    Context& context = Context::current();
+    Implementation::FramebufferState& state = context.state().framebuffer;
     if(state.readBinding == _id) state.readBinding = 0;
 
-    /* For draw binding reset also viewport */
+    /* For draw binding reset also viewport. Don't do that for windowless
+       contexts to avoid potential race conditions with default framebuffer on
+       another thread. */
     if(state.drawBinding == _id) {
         state.drawBinding = 0;
 
-        /**
-         * @todo Less ugly solution (need to call setViewportInternal() to
-         * reset the viewport to size of default framebuffer)
-         */
-        defaultFramebuffer.bind();
+        if(!(context.configurationFlags() & Context::Configuration::Flag::Windowless)) {
+            /**
+             * @todo Less ugly solution (need to call setViewportInternal() to
+             * reset the viewport to size of default framebuffer)
+             */
+            defaultFramebuffer.bind();
+        }
     }
 
     glDeleteFramebuffers(1, &_id);
diff --git a/src/Magnum/Platform/AbstractXApplication.h b/src/Magnum/Platform/AbstractXApplication.h
index fc91893a4..3b02f92f7 100644
--- a/src/Magnum/Platform/AbstractXApplication.h
+++ b/src/Magnum/Platform/AbstractXApplication.h
@@ -343,7 +343,9 @@ class AbstractXApplication::GLConfiguration: public GL::Context::Configuration {
         /**
          * @brief Context flag
          *
-         * Includes also everything from @ref GL::Context::Configuration::Flag.
+         * Includes also everything from @ref GL::Context::Configuration::Flag
+         * except for @relativeref{GL::Context::Configuration,Flag::Windowless},
+         * which is not meant to be enabled for windowed apps.
          * @see @ref Flags, @ref setFlags(), @ref GL::Context::Flag
          */
         enum class Flag: UnsignedLong {
diff --git a/src/Magnum/Platform/AndroidApplication.h b/src/Magnum/Platform/AndroidApplication.h
index d6055afad..11ea3d620 100644
--- a/src/Magnum/Platform/AndroidApplication.h
+++ b/src/Magnum/Platform/AndroidApplication.h
@@ -456,7 +456,9 @@ class AndroidApplication::GLConfiguration: public GL::Context::Configuration {
         /**
          * @brief Context flag
          *
-         * Includes also everything from @ref GL::Context::Configuration::Flag.
+         * Includes also everything from @ref GL::Context::Configuration::Flag
+         * except for @relativeref{GL::Context::Configuration,Flag::Windowless},
+         * which is not meant to be enabled for windowed apps.
          * @see @ref Flags, @ref setFlags(), @ref GL::Context::Flag
          */
         enum class Flag: UnsignedLong {
diff --git a/src/Magnum/Platform/EmscriptenApplication.h b/src/Magnum/Platform/EmscriptenApplication.h
index 585c24af1..fd76e5867 100644
--- a/src/Magnum/Platform/EmscriptenApplication.h
+++ b/src/Magnum/Platform/EmscriptenApplication.h
@@ -942,7 +942,9 @@ class EmscriptenApplication::GLConfiguration: public GL::Context::Configuration
         /**
          * @brief Context flag
          *
-         * Includes also everything from @ref GL::Context::Configuration::Flag.
+         * Includes also everything from @ref GL::Context::Configuration::Flag
+         * except for @relativeref{GL::Context::Configuration,Flag::Windowless},
+         * which is not meant to be enabled for windowed apps.
          * @see @ref Flags, @ref setFlags(), @ref GL::Context::Flag
          */
         enum class Flag: UnsignedLong {
diff --git a/src/Magnum/Platform/GlfwApplication.h b/src/Magnum/Platform/GlfwApplication.h
index 2d27a7180..c4f491665 100644
--- a/src/Magnum/Platform/GlfwApplication.h
+++ b/src/Magnum/Platform/GlfwApplication.h
@@ -784,7 +784,9 @@ class GlfwApplication::GLConfiguration: public GL::Context::Configuration {
         /**
          * @brief Context flag
          *
-         * Includes also everything from @ref GL::Context::Configuration::Flag.
+         * Includes also everything from @ref GL::Context::Configuration::Flag
+         * except for @relativeref{GL::Context::Configuration,Flag::Windowless},
+         * which is not meant to be enabled for windowed apps.
          * @see @ref Flags, @ref setFlags(), @ref GL::Context::Flag
          */
         enum class Flag: UnsignedLong {
diff --git a/src/Magnum/Platform/Sdl2Application.h b/src/Magnum/Platform/Sdl2Application.h
index acb6279be..4963f0a7f 100644
--- a/src/Magnum/Platform/Sdl2Application.h
+++ b/src/Magnum/Platform/Sdl2Application.h
@@ -1236,7 +1236,9 @@ class Sdl2Application::GLConfiguration: public GL::Context::Configuration {
         /**
          * @brief Context flag
          *
-         * Includes also everything from @ref GL::Context::Configuration::Flag.
+         * Includes also everything from @ref GL::Context::Configuration::Flag
+         * except for @relativeref{GL::Context::Configuration,Flag::Windowless},
+         * which is not meant to be enabled for windowed apps.
          * @see @ref Flags, @ref setFlags(), @ref GL::Context::Flag
          */
         enum class Flag: UnsignedLong {
diff --git a/src/Magnum/Platform/WindowlessCglApplication.cpp b/src/Magnum/Platform/WindowlessCglApplication.cpp
index 146780ab7..ed8efa5d4 100644
--- a/src/Magnum/Platform/WindowlessCglApplication.cpp
+++ b/src/Magnum/Platform/WindowlessCglApplication.cpp
@@ -105,6 +105,10 @@ bool WindowlessCglContext::release() {
     return false;
 }
 
+WindowlessCglContext::Configuration::Configuration() {
+    GL::Context::Configuration::addFlags(GL::Context::Configuration::Flag::Windowless);
+}
+
 #ifndef DOXYGEN_GENERATING_OUTPUT
 WindowlessCglApplication::WindowlessCglApplication(const Arguments& arguments): WindowlessCglApplication{arguments, Configuration{}} {}
 #endif
diff --git a/src/Magnum/Platform/WindowlessCglApplication.h b/src/Magnum/Platform/WindowlessCglApplication.h
index 20f8d8fda..ecb3dc915 100644
--- a/src/Magnum/Platform/WindowlessCglApplication.h
+++ b/src/Magnum/Platform/WindowlessCglApplication.h
@@ -166,7 +166,9 @@ class WindowlessCglContext::Configuration: public GL::Context::Configuration {
         /**
          * @brief Context flag
          *
-         * Includes also everything from @ref GL::Context::Configuration::Flag.
+         * Includes also everything from @ref GL::Context::Configuration::Flag
+         * except for @relativeref{GL::Context::Configuration,Flag::Windowless},
+         * which is enabled implicitly by default.
          * @see @ref Flags, @ref setFlags(), @ref GL::Context::Flag
          */
         enum class Flag: UnsignedLong {
@@ -196,6 +198,8 @@ class WindowlessCglContext::Configuration: public GL::Context::Configuration {
          */
         typedef Containers::EnumSet<Flag> Flags;
 
+        /*implicit*/ Configuration();
+
         /** @brief Context flags */
         Flags flags() const {
             return Flag(UnsignedLong(GL::Context::Configuration::flags()));
diff --git a/src/Magnum/Platform/WindowlessEglApplication.cpp b/src/Magnum/Platform/WindowlessEglApplication.cpp
index 9b8e3547b..347ef34d7 100644
--- a/src/Magnum/Platform/WindowlessEglApplication.cpp
+++ b/src/Magnum/Platform/WindowlessEglApplication.cpp
@@ -533,6 +533,7 @@ WindowlessEglContext::Configuration::Configuration()
     : _device{}
     #endif
 {
+    GL::Context::Configuration::addFlags(GL::Context::Configuration::Flag::Windowless);
     #ifndef MAGNUM_TARGET_GLES
     addFlags(Flag::ForwardCompatible);
     #endif
diff --git a/src/Magnum/Platform/WindowlessEglApplication.h b/src/Magnum/Platform/WindowlessEglApplication.h
index 6dbd46279..ecbe7c116 100644
--- a/src/Magnum/Platform/WindowlessEglApplication.h
+++ b/src/Magnum/Platform/WindowlessEglApplication.h
@@ -183,7 +183,9 @@ class WindowlessEglContext::Configuration: public GL::Context::Configuration {
         /**
          * @brief Context flag
          *
-         * Includes also everything from @ref GL::Context::Configuration::Flag.
+         * Includes also everything from @ref GL::Context::Configuration::Flag
+         * except for @relativeref{GL::Context::Configuration,Flag::Windowless},
+         * which is enabled implicitly by default.
          * @see @ref Flags, @ref setFlags(), @ref GL::Context::Flag
          */
         enum class Flag: UnsignedLong {
diff --git a/src/Magnum/Platform/WindowlessGlxApplication.cpp b/src/Magnum/Platform/WindowlessGlxApplication.cpp
index 0d0cb3fb4..01bea105a 100644
--- a/src/Magnum/Platform/WindowlessGlxApplication.cpp
+++ b/src/Magnum/Platform/WindowlessGlxApplication.cpp
@@ -274,6 +274,7 @@ bool WindowlessGlxContext::release() {
 }
 
 WindowlessGlxContext::Configuration::Configuration() {
+    GL::Context::Configuration::addFlags(GL::Context::Configuration::Flag::Windowless);
     #ifndef MAGNUM_TARGET_GLES
     addFlags(Flag::ForwardCompatible);
     #endif
diff --git a/src/Magnum/Platform/WindowlessGlxApplication.h b/src/Magnum/Platform/WindowlessGlxApplication.h
index 639625be5..158f19edf 100644
--- a/src/Magnum/Platform/WindowlessGlxApplication.h
+++ b/src/Magnum/Platform/WindowlessGlxApplication.h
@@ -188,7 +188,9 @@ class WindowlessGlxContext::Configuration: public GL::Context::Configuration {
         /**
          * @brief Context flag
          *
-         * Includes also everything from @ref GL::Context::Configuration::Flag.
+         * Includes also everything from @ref GL::Context::Configuration::Flag
+         * except for @relativeref{GL::Context::Configuration,Flag::Windowless},
+         * which is enabled implicitly by default.
          * @see @ref Flags, @ref setFlags(), @ref GL::Context::Flag
          */
         enum class Flag: UnsignedLong {
diff --git a/src/Magnum/Platform/WindowlessIosApplication.h b/src/Magnum/Platform/WindowlessIosApplication.h
index 472e6d92f..5b55b2643 100644
--- a/src/Magnum/Platform/WindowlessIosApplication.h
+++ b/src/Magnum/Platform/WindowlessIosApplication.h
@@ -157,7 +157,9 @@ class WindowlessIosContext::Configuration: public GL::Context::Configuration {
         /**
          * @brief Context flag
          *
-         * Includes also everything from @ref GL::Context::Configuration::Flag.
+         * Includes also everything from @ref GL::Context::Configuration::Flag
+         * except for @relativeref{GL::Context::Configuration,Flag::Windowless},
+         * which is enabled implicitly by default.
          * @see @ref Flags, @ref setFlags(), @ref GL::Context::Flag
          */
         enum class Flag: UnsignedLong {
@@ -187,6 +189,8 @@ class WindowlessIosContext::Configuration: public GL::Context::Configuration {
          */
         typedef Containers::EnumSet<Flag> Flags;
 
+        /*implicit*/ Configuration();
+
         /** @brief Context flags */
         Flags flags() const {
             return Flag(UnsignedLong(GL::Context::Configuration::flags()));
diff --git a/src/Magnum/Platform/WindowlessIosApplication.mm b/src/Magnum/Platform/WindowlessIosApplication.mm
index a174de8e2..c3778778f 100644
--- a/src/Magnum/Platform/WindowlessIosApplication.mm
+++ b/src/Magnum/Platform/WindowlessIosApplication.mm
@@ -82,6 +82,10 @@ bool WindowlessIosContext::release() {
     return false;
 }
 
+WindowlessIosContext::Configuration::Configuration() {
+    GL::Context::Configuration::addFlags(GL::Context::Configuration::Flag::Windowless);
+}
+
 #ifndef DOXYGEN_GENERATING_OUTPUT
 WindowlessIosApplication::WindowlessIosApplication(const Arguments& arguments): WindowlessIosApplication{arguments, Configuration{}} {}
 #endif
diff --git a/src/Magnum/Platform/WindowlessWglApplication.cpp b/src/Magnum/Platform/WindowlessWglApplication.cpp
index 5f9482f3c..493e94b26 100644
--- a/src/Magnum/Platform/WindowlessWglApplication.cpp
+++ b/src/Magnum/Platform/WindowlessWglApplication.cpp
@@ -259,6 +259,7 @@ bool WindowlessWglContext::release() {
 }
 
 WindowlessWglContext::Configuration::Configuration() {
+    GL::Context::Configuration::addFlags(GL::Context::Configuration::Flag::Windowless);
     #ifndef MAGNUM_TARGET_GLES
     addFlags(Flag::ForwardCompatible);
     #endif
diff --git a/src/Magnum/Platform/WindowlessWglApplication.h b/src/Magnum/Platform/WindowlessWglApplication.h
index 71db719f2..067369fcc 100644
--- a/src/Magnum/Platform/WindowlessWglApplication.h
+++ b/src/Magnum/Platform/WindowlessWglApplication.h
@@ -175,7 +175,9 @@ class WindowlessWglContext::Configuration: public GL::Context::Configuration {
         /**
          * @brief Context flag
          *
-         * Includes also everything from @ref GL::Context::Configuration::Flag.
+         * Includes also everything from @ref GL::Context::Configuration::Flag
+         * except for @relativeref{GL::Context::Configuration,Flag::Windowless},
+         * which is enabled implicitly by default.
          * @see @ref Flags, @ref setFlags(), @ref GL::Context::Flag
          */
         enum class Flag: UnsignedLong {
diff --git a/src/Magnum/Platform/WindowlessWindowsEglApplication.cpp b/src/Magnum/Platform/WindowlessWindowsEglApplication.cpp
index b153ac85d..5eac49ebe 100644
--- a/src/Magnum/Platform/WindowlessWindowsEglApplication.cpp
+++ b/src/Magnum/Platform/WindowlessWindowsEglApplication.cpp
@@ -182,6 +182,10 @@ bool WindowlessWindowsEglContext::release() {
     return false;
 }
 
+WindowlessWindowsEglContext::Configuration::Configuration() {
+    GL::Context::Configuration::addFlags(GL::Context::Configuration::Flag::Windowless);
+}
+
 #ifndef DOXYGEN_GENERATING_OUTPUT
 WindowlessWindowsEglApplication::WindowlessWindowsEglApplication(const Arguments& arguments): WindowlessWindowsEglApplication{arguments, Configuration{}} {}
 #endif
diff --git a/src/Magnum/Platform/WindowlessWindowsEglApplication.h b/src/Magnum/Platform/WindowlessWindowsEglApplication.h
index 64c4701bc..7268ad2b8 100644
--- a/src/Magnum/Platform/WindowlessWindowsEglApplication.h
+++ b/src/Magnum/Platform/WindowlessWindowsEglApplication.h
@@ -161,7 +161,9 @@ class WindowlessWindowsEglContext::Configuration: public GL::Context::Configurat
         /**
          * @brief Context flag
          *
-         * Includes also everything from @ref GL::Context::Configuration::Flag.
+         * Includes also everything from @ref GL::Context::Configuration::Flag
+         * except for @relativeref{GL::Context::Configuration,Flag::Windowless},
+         * which is enabled implicitly by default.
          * @see @ref Flags, @ref setFlags(), @ref GL::Context::Flag
          */
         enum class Flag: UnsignedLong {
@@ -199,6 +201,8 @@ class WindowlessWindowsEglContext::Configuration: public GL::Context::Configurat
          */
         typedef Containers::EnumSet<Flag> Flags;
 
+        /*implicit*/ Configuration();
+
         /** @brief Context flags */
         Flags flags() const {
             return Flag(UnsignedLong(GL::Context::Configuration::flags()));