diff --git a/ui/cocoa/ebiten_window.c b/ui/cocoa/ebiten_window.c
index 6e4b09578..460708522 100644
--- a/ui/cocoa/ebiten_window.c
+++ b/ui/cocoa/ebiten_window.c
@@ -2,10 +2,10 @@
 
 #import "ebiten_window.h"
 
-#include <OpenGL/gl.h>
-
 #import "ebiten_content_view.h"
 
+@class NSOpenGLContext;
+
 void ebiten_WindowClosed(void* nativeWindow);
 
 @implementation EbitenWindow {
@@ -16,6 +16,7 @@ void ebiten_WindowClosed(void* nativeWindow);
 - (id)initWithSize:(NSSize)size
          glContext:(NSOpenGLContext*)glContext {
   self->glContext_ = glContext;
+  [self->glContext_ retain];
 
   NSUInteger style = (NSTitledWindowMask | NSClosableWindowMask |
                       NSMiniaturizableWindowMask);
@@ -35,14 +36,16 @@ void ebiten_WindowClosed(void* nativeWindow);
                           styleMask:style
                             backing:NSBackingStoreBuffered
                               defer:YES];
-  assert(self != nil);
-  [self setReleasedWhenClosed:YES];
-  [self setDelegate:self];
-  [self setDocumentEdited:YES];
+  if (self != nil) {
+    [self setReleasedWhenClosed:YES];
+    [self setDelegate:self];
+    [self setDocumentEdited:YES];
 
-  NSRect rect = NSMakeRect(0, 0, size.width, size.height);
-  NSView* contentView = [[EbitenContentView alloc] initWithFrame:rect];
-  [self setContentView:contentView];
+    NSRect rect = NSMakeRect(0, 0, size.width, size.height);
+    NSView* contentView = [[EbitenContentView alloc] initWithFrame:rect];
+    [self setContentView:contentView];
+    [contentView release];
+  }
 
   return self;
 }
diff --git a/ui/cocoa/mainloop.c b/ui/cocoa/mainloop.c
index 771d9c4a4..8f54a39de 100644
--- a/ui/cocoa/mainloop.c
+++ b/ui/cocoa/mainloop.c
@@ -54,11 +54,15 @@ void* CreateWindow(size_t width, size_t height, const char* title, void* glConte
   EbitenWindow* window = [[EbitenWindow alloc]
                             initWithSize:size
                                glContext:glContext];
-  [window setTitle: [[NSString alloc]
-                      initWithUTF8String:title]];
+  NSString* nsTitle = [[NSString alloc]
+                      initWithUTF8String:title];
+  [window setTitle: nsTitle];
+  [nsTitle release];
+
   [window makeKeyAndOrderFront:nil];
 
-  [(NSOpenGLContext*)glContext setView:[window contentView]];
+  [glContext setView:[window contentView]];
+  [glContext release];
 
   return window;
 }