diff --git a/amdgpu.c b/amdgpu.c
index ff1336d..da11081 100644
--- a/amdgpu.c
+++ b/amdgpu.c
@@ -436,6 +436,7 @@ struct backend backend_amdgpu = {
 	.bo_destroy = drv_gem_bo_destroy,
 	.bo_import = drv_prime_bo_import,
 	.bo_map = amdgpu_bo_map,
+	.bo_unmap = drv_bo_munmap,
 	.resolve_format = amdgpu_resolve_format,
 };
 
diff --git a/cirrus.c b/cirrus.c
index 4f0e983..d92bab4 100644
--- a/cirrus.c
+++ b/cirrus.c
@@ -29,4 +29,5 @@ struct backend backend_cirrus = {
 	.bo_destroy = drv_dumb_bo_destroy,
 	.bo_import = drv_prime_bo_import,
 	.bo_map = drv_dumb_bo_map,
+	.bo_unmap = drv_bo_munmap,
 };
diff --git a/drv.c b/drv.c
index 92e9b24..ff99893 100644
--- a/drv.c
+++ b/drv.c
@@ -429,10 +429,7 @@ int drv_bo_unmap(struct bo *bo, struct map_info *data)
 	pthread_mutex_lock(&bo->drv->driver_lock);
 
 	if (!--data->refcount) {
-		if (bo->drv->backend->bo_unmap)
-			ret = bo->drv->backend->bo_unmap(bo, data);
-		else
-			ret = munmap(data->addr, data->length);
+		ret = bo->drv->backend->bo_unmap(bo, data);
 		drmHashDelete(bo->drv->map_table, data->handle);
 		free(data);
 	}
diff --git a/evdi.c b/evdi.c
index f66fb2d..829d6ea 100644
--- a/evdi.c
+++ b/evdi.c
@@ -28,4 +28,5 @@ struct backend backend_evdi = {
 	.bo_destroy = drv_dumb_bo_destroy,
 	.bo_import = drv_prime_bo_import,
 	.bo_map = drv_dumb_bo_map,
+	.bo_unmap = drv_bo_munmap,
 };
diff --git a/exynos.c b/exynos.c
index 0d935eb..b21cc2b 100644
--- a/exynos.c
+++ b/exynos.c
@@ -112,6 +112,7 @@ struct backend backend_exynos = {
 	.bo_destroy = drv_gem_bo_destroy,
 	.bo_import = drv_prime_bo_import,
 	.bo_map = drv_dumb_bo_map,
+	.bo_unmap = drv_bo_munmap,
 };
 
 #endif
diff --git a/gma500.c b/gma500.c
index 5b08bc3..c3f3c12 100644
--- a/gma500.c
+++ b/gma500.c
@@ -28,4 +28,5 @@ struct backend backend_gma500 = {
 	.bo_destroy = drv_dumb_bo_destroy,
 	.bo_import = drv_prime_bo_import,
 	.bo_map = drv_dumb_bo_map,
+	.bo_unmap = drv_bo_munmap,
 };
diff --git a/helpers.c b/helpers.c
index 0a09b5a..9d72a6c 100644
--- a/helpers.c
+++ b/helpers.c
@@ -313,6 +313,11 @@ void *drv_dumb_bo_map(struct bo *bo, struct map_info *data, size_t plane, int pr
 	return mmap(0, data->length, prot, MAP_SHARED, bo->drv->fd, map_dumb.offset);
 }
 
+int drv_bo_munmap(struct bo *bo, struct map_info *data)
+{
+	return munmap(data->addr, data->length);
+}
+
 uintptr_t drv_get_reference_count(struct driver *drv, struct bo *bo, size_t plane)
 {
 	void *count;
diff --git a/helpers.h b/helpers.h
index dc1a7c0..b580643 100644
--- a/helpers.h
+++ b/helpers.h
@@ -17,6 +17,7 @@ int drv_dumb_bo_destroy(struct bo *bo);
 int drv_gem_bo_destroy(struct bo *bo);
 int drv_prime_bo_import(struct bo *bo, struct drv_import_fd_data *data);
 void *drv_dumb_bo_map(struct bo *bo, struct map_info *data, size_t plane, int prot);
+int drv_bo_munmap(struct bo *bo, struct map_info *data);
 uintptr_t drv_get_reference_count(struct driver *drv, struct bo *bo, size_t plane);
 void drv_increment_reference_count(struct driver *drv, struct bo *bo, size_t plane);
 void drv_decrement_reference_count(struct driver *drv, struct bo *bo, size_t plane);
diff --git a/marvell.c b/marvell.c
index 8114ac7..455b033 100644
--- a/marvell.c
+++ b/marvell.c
@@ -31,6 +31,7 @@ struct backend backend_marvell = {
 	.bo_destroy = drv_dumb_bo_destroy,
 	.bo_import = drv_prime_bo_import,
 	.bo_map = drv_dumb_bo_map,
+	.bo_unmap = drv_bo_munmap,
 };
 
 #endif
diff --git a/nouveau.c b/nouveau.c
index 7cdab3a..e8a02e3 100644
--- a/nouveau.c
+++ b/nouveau.c
@@ -28,4 +28,5 @@ struct backend backend_nouveau = {
 	.bo_destroy = drv_dumb_bo_destroy,
 	.bo_import = drv_prime_bo_import,
 	.bo_map = drv_dumb_bo_map,
+	.bo_unmap = drv_bo_munmap,
 };
diff --git a/radeon.c b/radeon.c
index baf42ed..3af0be1 100644
--- a/radeon.c
+++ b/radeon.c
@@ -28,4 +28,5 @@ struct backend backend_radeon = {
 	.bo_destroy = drv_dumb_bo_destroy,
 	.bo_import = drv_prime_bo_import,
 	.bo_map = drv_dumb_bo_map,
+	.bo_unmap = drv_bo_munmap,
 };
diff --git a/udl.c b/udl.c
index eb15fbe..dc3c4eb 100644
--- a/udl.c
+++ b/udl.c
@@ -28,4 +28,5 @@ struct backend backend_udl = {
 	.bo_destroy = drv_dumb_bo_destroy,
 	.bo_import = drv_prime_bo_import,
 	.bo_map = drv_dumb_bo_map,
+	.bo_unmap = drv_bo_munmap,
 };
diff --git a/vc4.c b/vc4.c
index c797bd9..6dca979 100644
--- a/vc4.c
+++ b/vc4.c
@@ -87,6 +87,7 @@ struct backend backend_vc4 = {
 	.bo_import = drv_prime_bo_import,
 	.bo_destroy = drv_gem_bo_destroy,
 	.bo_map = vc4_bo_map,
+	.bo_unmap = drv_bo_munmap,
 };
 
 #endif
diff --git a/vgem.c b/vgem.c
index 4e6eefb..0152b47 100644
--- a/vgem.c
+++ b/vgem.c
@@ -67,5 +67,6 @@ struct backend backend_vgem = {
 	.bo_destroy = drv_dumb_bo_destroy,
 	.bo_import = drv_prime_bo_import,
 	.bo_map = drv_dumb_bo_map,
+	.bo_unmap = drv_bo_munmap,
 	.resolve_format = vgem_resolve_format,
 };
diff --git a/virtio_gpu.c b/virtio_gpu.c
index fe580cd..afdb5a2 100644
--- a/virtio_gpu.c
+++ b/virtio_gpu.c
@@ -67,5 +67,6 @@ struct backend backend_virtio_gpu = {
 	.bo_destroy = drv_dumb_bo_destroy,
 	.bo_import = drv_prime_bo_import,
 	.bo_map = drv_dumb_bo_map,
+	.bo_unmap = drv_bo_munmap,
 	.resolve_format = virtio_gpu_resolve_format,
 };