diff --git a/internal/graphicsdriver/metal/ca/ca.h b/internal/graphicsdriver/metal/ca/ca.h
index d470eed34..a4e1e35d5 100644
--- a/internal/graphicsdriver/metal/ca/ca.h
+++ b/internal/graphicsdriver/metal/ca/ca.h
@@ -16,14 +16,13 @@
 
 #include <stdint.h>
 
-typedef signed char BOOL;
 typedef unsigned long uint_t;
 
 void *MakeMetalLayer();
 
 uint16_t MetalLayer_PixelFormat(void *metalLayer);
 void MetalLayer_SetDevice(void *metalLayer, void *device);
-void MetalLayer_SetOpaque(void *metalLayer, BOOL opaque);
+void MetalLayer_SetOpaque(void *metalLayer, unsigned char opaque);
 const char *MetalLayer_SetPixelFormat(void *metalLayer, uint16_t pixelFormat);
 const char *MetalLayer_SetMaximumDrawableCount(void *metalLayer,
                                                uint_t maximumDrawableCount);
diff --git a/internal/graphicsdriver/metal/ca/ca.m b/internal/graphicsdriver/metal/ca/ca.m
index 3ce535d58..2ae631835 100644
--- a/internal/graphicsdriver/metal/ca/ca.m
+++ b/internal/graphicsdriver/metal/ca/ca.m
@@ -38,8 +38,8 @@ void MetalLayer_SetDevice(void *metalLayer, void *device) {
   ((CAMetalLayer *)metalLayer).device = (id<MTLDevice>)device;
 }
 
-void MetalLayer_SetOpaque(void *metalLayer, BOOL opaque) {
-  ((CAMetalLayer *)metalLayer).opaque = opaque;
+void MetalLayer_SetOpaque(void *metalLayer, unsigned char opaque) {
+  ((CAMetalLayer *)metalLayer).opaque = (BOOL)opaque;
 }
 
 const char *MetalLayer_SetPixelFormat(void *metalLayer, uint16_t pixelFormat) {
diff --git a/internal/graphicsdriver/metal/ns/ns.h b/internal/graphicsdriver/metal/ns/ns.h
index 7962023e6..ca9c4c078 100644
--- a/internal/graphicsdriver/metal/ns/ns.h
+++ b/internal/graphicsdriver/metal/ns/ns.h
@@ -14,11 +14,7 @@
 
 // +build darwin
 
-#include <stdint.h>
-
-typedef signed char BOOL;
-
 void *Window_ContentView(void *window);
 
 void View_SetLayer(void *view, void *layer);
-void View_SetWantsLayer(void *view, BOOL wantsLayer);
+void View_SetWantsLayer(void *view, unsigned char wantsLayer);
diff --git a/internal/graphicsdriver/metal/ns/ns.m b/internal/graphicsdriver/metal/ns/ns.m
index c4a820bcf..55fb09e38 100644
--- a/internal/graphicsdriver/metal/ns/ns.m
+++ b/internal/graphicsdriver/metal/ns/ns.m
@@ -25,6 +25,6 @@ void View_SetLayer(void *view, void *layer) {
   ((NSView *)view).layer = (CALayer *)layer;
 }
 
-void View_SetWantsLayer(void *view, BOOL wantsLayer) {
-  ((NSView *)view).wantsLayer = wantsLayer;
+void View_SetWantsLayer(void *view, unsigned char wantsLayer) {
+  ((NSView *)view).wantsLayer = (BOOL)wantsLayer;
 }