diff --git a/android/cpp/native_map_view.cpp b/android/cpp/native_map_view.cpp
index 4cd1669ef..03530aeff 100644
--- a/android/cpp/native_map_view.cpp
+++ b/android/cpp/native_map_view.cpp
@@ -17,10 +17,6 @@
 #include <mbgl/platform/gl.hpp>
 #include <mbgl/util/std.hpp>
 
-#include <pthread.h>
-
-pthread_once_t loadGLExtensions = PTHREAD_ONCE_INIT;
-
 namespace mbgl {
 namespace android {
 
@@ -308,8 +304,6 @@ void NativeMapView::terminateContext() {
     context = EGL_NO_CONTEXT;
 }
 
-void loadExtensions();
-
 void NativeMapView::createSurface(ANativeWindow *window_) {
     mbgl::Log::Debug(mbgl::Event::Android, "NativeMapView::createSurface");
 
@@ -349,9 +343,11 @@ void NativeMapView::createSurface(ANativeWindow *window_) {
                         "SL Version"); // In the emulator this returns NULL with error code 0?
                                         // https://code.google.com/p/android/issues/detail?id=78977
         }
-        log_gl_string(GL_EXTENSIONS, "Extensions");
 
-        pthread_once(&loadGLExtensions, loadExtensions);
+        log_gl_string(GL_EXTENSIONS, "Extensions");
+        mbgl::gl::InitializeExtensions([] (const char * name) {
+             return reinterpret_cast<mbgl::gl::glProc>(eglGetProcAddress(name));
+        });
 
         if (!eglMakeCurrent(display, EGL_NO_SURFACE, EGL_NO_SURFACE, EGL_NO_CONTEXT)) {
             mbgl::Log::Error(mbgl::Event::OpenGL,
@@ -584,12 +580,6 @@ EGLConfig NativeMapView::chooseConfig(const EGLConfig configs[], EGLint numConfi
     return configId;
 }
 
-void loadExtensions() {
-    mbgl::gl::InitializeExtensions([] (const char * name) {
-         return reinterpret_cast<mbgl::gl::glProc>(eglGetProcAddress(name));
-    });
-}
-
 void NativeMapView::pause() {
     mbgl::Log::Debug(mbgl::Event::Android, "NativeMapView::pause");
 
diff --git a/platform/default/glfw_view.cpp b/platform/default/glfw_view.cpp
index ed499d374..8265bb8bb 100644
--- a/platform/default/glfw_view.cpp
+++ b/platform/default/glfw_view.cpp
@@ -4,9 +4,6 @@
 #include <mbgl/util/gl_helper.hpp>
 
 #include <cassert>
-#include <pthread.h>
-
-pthread_once_t loadGLExtensions = PTHREAD_ONCE_INIT;
 
 void glfwError(int error, const char *description) {
     mbgl::Log::Error(mbgl::Event::OpenGL, "GLFW error (%i): %s", error, description);
@@ -61,9 +58,7 @@ GLFWView::GLFWView(bool fullscreen_) : fullscreen(fullscreen_) {
     glfwSetScrollCallback(window, onScroll);
     glfwSetKeyCallback(window, onKey);
 
-    pthread_once(&loadGLExtensions, [] {
-        mbgl::gl::InitializeExtensions(glfwGetProcAddress);
-    });
+    mbgl::gl::InitializeExtensions(glfwGetProcAddress);
 
     glfwMakeContextCurrent(nullptr);
 }
diff --git a/platform/default/headless_view.cpp b/platform/default/headless_view.cpp
index 357c6fac7..aa07706d8 100644
--- a/platform/default/headless_view.cpp
+++ b/platform/default/headless_view.cpp
@@ -13,8 +13,6 @@
 #include <cstring>
 #include <cassert>
 
-pthread_once_t loadGLExtensions = PTHREAD_ONCE_INIT;
-
 #ifdef MBGL_USE_CGL
 #include <CoreFoundation/CoreFoundation.h>
 #elif MBGL_USE_GLX
@@ -45,28 +43,26 @@ void HeadlessView::loadExtensions() {
         return;
     }
 
-    pthread_once(&loadGLExtensions, [] {
 #ifdef MBGL_USE_CGL
-        gl::InitializeExtensions([](const char * name) {
-            static CFBundleRef framework = CFBundleGetBundleWithIdentifier(CFSTR("com.apple.opengl"));
-            if (!framework) {
-                throw std::runtime_error("Failed to load OpenGL framework.");
-            }
+    gl::InitializeExtensions([](const char * name) {
+        static CFBundleRef framework = CFBundleGetBundleWithIdentifier(CFSTR("com.apple.opengl"));
+        if (!framework) {
+            throw std::runtime_error("Failed to load OpenGL framework.");
+        }
 
-            CFStringRef str = CFStringCreateWithCString(kCFAllocatorDefault, name, kCFStringEncodingASCII);
-            void* symbol = CFBundleGetFunctionPointerForName(framework, str);
-            CFRelease(str);
+        CFStringRef str = CFStringCreateWithCString(kCFAllocatorDefault, name, kCFStringEncodingASCII);
+        void* symbol = CFBundleGetFunctionPointerForName(framework, str);
+        CFRelease(str);
 
-            return reinterpret_cast<gl::glProc>(symbol);
-        });
+        return reinterpret_cast<gl::glProc>(symbol);
+    });
 #endif
 
 #ifdef MBGL_USE_GLX
-        gl::InitializeExtensions([](const char * name) {
-            return glXGetProcAddress(reinterpret_cast<const GLubyte *>(name));
-        });
-#endif
+    gl::InitializeExtensions([](const char * name) {
+        return glXGetProcAddress(reinterpret_cast<const GLubyte *>(name));
     });
+#endif
 
     extensionsLoaded = true;
 }
diff --git a/platform/ios/MGLMapView.mm b/platform/ios/MGLMapView.mm
index a2e55b337..586ceb20f 100644
--- a/platform/ios/MGLMapView.mm
+++ b/platform/ios/MGLMapView.mm
@@ -35,8 +35,6 @@
 
 class MBGLView;
 
-static dispatch_once_t loadGLExtensions;
-
 NSString *const MGLDefaultStyleName = @"mapbox-streets";
 NSString *const MGLStyleVersion = @"7";
 NSString *const MGLDefaultStyleMarkerSymbolName = @"default_marker";
@@ -233,20 +231,17 @@ std::chrono::steady_clock::duration secondsAsDuration(float duration)
 
     // load extensions
     //
-    dispatch_once(&loadGLExtensions, ^
-    {
-        mbgl::gl::InitializeExtensions([](const char * name) {
-            static CFBundleRef framework = CFBundleGetBundleWithIdentifier(CFSTR("com.apple.opengles"));
-            if (!framework) {
-                throw std::runtime_error("Failed to load OpenGL framework.");
-            }
+    mbgl::gl::InitializeExtensions([](const char * name) {
+        static CFBundleRef framework = CFBundleGetBundleWithIdentifier(CFSTR("com.apple.opengles"));
+        if (!framework) {
+            throw std::runtime_error("Failed to load OpenGL framework.");
+        }
 
-            CFStringRef str = CFStringCreateWithCString(kCFAllocatorDefault, name, kCFStringEncodingASCII);
-            void* symbol = CFBundleGetFunctionPointerForName(framework, str);
-            CFRelease(str);
+        CFStringRef str = CFStringCreateWithCString(kCFAllocatorDefault, name, kCFStringEncodingASCII);
+        void* symbol = CFBundleGetFunctionPointerForName(framework, str);
+        CFRelease(str);
 
-            return reinterpret_cast<mbgl::gl::glProc>(symbol);
-        });
+        return reinterpret_cast<mbgl::gl::glProc>(symbol);
     });
 
     // setup mbgl map
diff --git a/src/mbgl/platform/gl.cpp b/src/mbgl/platform/gl.cpp
index 3d8a237c7..76be580b9 100644
--- a/src/mbgl/platform/gl.cpp
+++ b/src/mbgl/platform/gl.cpp
@@ -1,5 +1,7 @@
 #include <mbgl/platform/gl.hpp>
 
+#include <mutex>
+
 namespace mbgl {
 namespace gl {
 
@@ -8,22 +10,26 @@ std::vector<ExtensionFunctionBase*>& ExtensionFunctionBase::functions() {
     return functions;
 }
 
+static std::once_flag initializeExtensionsOnce;
+
 void InitializeExtensions(glProc (*getProcAddress)(const char *)) {
-    const char * extensionsPtr = reinterpret_cast<const char *>(
-        MBGL_CHECK_ERROR(glGetString(GL_EXTENSIONS)));
+    std::call_once(initializeExtensionsOnce, [getProcAddress] {
+        const char * extensionsPtr = reinterpret_cast<const char *>(
+            MBGL_CHECK_ERROR(glGetString(GL_EXTENSIONS)));
 
-    if (!extensionsPtr)
-        return;
+        if (!extensionsPtr)
+            return;
 
-    const std::string extensions = extensionsPtr;
-    for (auto fn : ExtensionFunctionBase::functions()) {
-        for (auto probe : fn->probes) {
-            if (extensions.find(probe.first) != std::string::npos) {
-                fn->ptr = getProcAddress(probe.second);
-                break;
+        const std::string extensions = extensionsPtr;
+        for (auto fn : ExtensionFunctionBase::functions()) {
+            for (auto probe : fn->probes) {
+                if (extensions.find(probe.first) != std::string::npos) {
+                    fn->ptr = getProcAddress(probe.second);
+                    break;
+                }
             }
         }
-    }
+    });
 }
 
 void checkError(const char *cmd, const char *file, int line) {