diff --git a/src/macosx/MacMiniFB.m b/src/macosx/MacMiniFB.m
index 41234c4..6b7ab38 100644
--- a/src/macosx/MacMiniFB.m
+++ b/src/macosx/MacMiniFB.m
@@ -21,13 +21,6 @@ void init_keycodes();
 id<MTLDevice>  g_metal_device = nil;
 id<MTLLibrary> g_library      = nil;
 
-Vertex g_vertices[4] = {
-    {-1.0, -1.0, 0, 1},
-    {-1.0,  1.0, 0, 1},
-    { 1.0, -1.0, 0, 1},
-    { 1.0,  1.0, 0, 1},
-};
-
 //-------------------------------------
 #define kShader(inc, src)    @inc#src
 
@@ -185,6 +178,14 @@ mfb_open_ex(const char *title, unsigned width, unsigned height, unsigned flags)
     if (!window_data->draw_buffer)
         return 0x0;
 
+    static Vertex s_vertices[4] = {
+        {-1.0, -1.0, 0, 1},
+        {-1.0,  1.0, 0, 1},
+        { 1.0, -1.0, 0, 1},
+        { 1.0,  1.0, 0, 1},
+    };
+    memcpy(window_data_osx->metal.vertices, s_vertices, sizeof(s_vertices));
+
     // Setup command queue
     window_data_osx->metal.command_queue = [g_metal_device newCommandQueue];
 
@@ -431,17 +432,19 @@ mfb_set_viewport(struct mfb_window *window, unsigned offset_x, unsigned offset_y
     float y1 =  ((float) offset_y           / window_data->window_height) * 2.0f - 1.0f;
     float y2 = (((float) offset_y + height) / window_data->window_height) * 2.0f - 1.0f;
 
-    g_vertices[0].x = x1;
-    g_vertices[0].y = y1;
+    SWindowData_OSX *window_data_osx = (SWindowData_OSX *) window_data->specific;
 
-    g_vertices[1].x = x1;
-    g_vertices[1].y = y2;
+    window_data_osx->metal.vertices[0].x = x1;
+    window_data_osx->metal.vertices[0].y = y1;
 
-    g_vertices[2].x = x2;
-    g_vertices[2].y = y1;
+    window_data_osx->metal.vertices[1].x = x1;
+    window_data_osx->metal.vertices[1].y = y2;
 
-    g_vertices[3].x = x2;
-    g_vertices[3].y = y2;
+    window_data_osx->metal.vertices[2].x = x2;
+    window_data_osx->metal.vertices[2].y = y1;
+
+    window_data_osx->metal.vertices[3].x = x2;
+    window_data_osx->metal.vertices[3].y = y2;
 #endif
 
     return true;
diff --git a/src/macosx/OSXWindowFrameView.h b/src/macosx/OSXWindowFrameView.h
index ad3b308..8636e09 100644
--- a/src/macosx/OSXWindowFrameView.h
+++ b/src/macosx/OSXWindowFrameView.h
@@ -5,10 +5,6 @@
 #if defined(USE_METAL_API)
 #import <MetalKit/MetalKit.h>
 
-typedef struct Vertex {
-    float x, y, z, w;
-} Vertex;
-
 // Number of textures in flight (tripple buffered)
 enum { MaxBuffersInFlight = 3 };
 
diff --git a/src/macosx/OSXWindowFrameView.m b/src/macosx/OSXWindowFrameView.m
index 1f5764a..2f678f3 100644
--- a/src/macosx/OSXWindowFrameView.m
+++ b/src/macosx/OSXWindowFrameView.m
@@ -9,8 +9,6 @@
 extern id<MTLDevice>  g_metal_device;
 extern id<MTLLibrary> g_library;
 
-extern Vertex g_vertices[4];
-
 @implementation WindowViewController
 
 - (void) mtkView:(nonnull MTKView *)view drawableSizeWillChange:(CGSize)size {
@@ -69,7 +67,7 @@ extern Vertex g_vertices[4];
         SWindowData_OSX *window_data_osx = (SWindowData_OSX *) window->window_data->specific;
         [renderEncoder setRenderPipelineState:window_data_osx->metal.pipeline_state];
 
-        [renderEncoder setVertexBytes:g_vertices length:sizeof(g_vertices) atIndex:0];
+        [renderEncoder setVertexBytes:window_data_osx->metal.vertices length:sizeof(window_data_osx->metal.vertices) atIndex:0];
 
         [renderEncoder setFragmentTexture:texture_buffers[current_buffer] atIndex:0];
 
diff --git a/src/macosx/WindowData_OSX.h b/src/macosx/WindowData_OSX.h
index ec8bd5f..09f8aba 100644
--- a/src/macosx/WindowData_OSX.h
+++ b/src/macosx/WindowData_OSX.h
@@ -9,6 +9,10 @@
 
 @class OSXWindow;
 
+typedef struct Vertex {
+    float x, y, z, w;
+} Vertex;
+
 typedef struct {
     OSXWindow           *window;
     struct mfb_timer    *timer;
@@ -17,6 +21,7 @@ typedef struct {
     struct {
         id<MTLCommandQueue>         command_queue;
         id<MTLRenderPipelineState>  pipeline_state; 
+        Vertex                      vertices[4];
     } metal;
 #endif        
 } SWindowData_OSX;
diff --git a/tests/multiple_windows.c b/tests/multiple_windows.c
index da391da..caab598 100644
--- a/tests/multiple_windows.c
+++ b/tests/multiple_windows.c
@@ -107,7 +107,7 @@ main()
     mfb_set_mouse_scroll_callback(window_a, mouse_scroll);
 
     mfb_set_user_data(window_a, (void *) "Window A");
-    mfb_set_viewport(window_a, 25, 25, WIDTH_A-25, HEIGHT_A-25);
+    mfb_set_viewport(window_a, 25, 25, WIDTH_A-50, HEIGHT_A-50);
 
     //--
     struct mfb_window *window_b = mfb_open_ex("Secondary Window", WIDTH_B, HEIGHT_B, WF_RESIZABLE);