diff --git a/filament/backend/src/CircularBuffer.cpp b/filament/backend/src/CircularBuffer.cpp
index 86bee8d6b1..0d298d2c27 100644
--- a/filament/backend/src/CircularBuffer.cpp
+++ b/filament/backend/src/CircularBuffer.cpp
@@ -90,19 +90,24 @@ void* CircularBuffer::alloc(size_t size) noexcept {
 
     if (UTILS_UNLIKELY(mUsesAshmem < 0)) {
         // ashmem failed
-        if (vaddr_guard != MAP_FAILED)
+        if (vaddr_guard != MAP_FAILED) {
             munmap(vaddr_guard, size);
+        }
 
-        if (vaddr_shadow != MAP_FAILED)
+        if (vaddr_shadow != MAP_FAILED) {
             munmap(vaddr_shadow, size);
+        }
 
-        if (vaddr != MAP_FAILED)
+        if (vaddr != MAP_FAILED) {
             munmap(vaddr, size);
+        }
 
-        if (fd >= 0)
+        if (fd >= 0) {
             close(fd);
+        }
 
-        data = mmap(nullptr, size * 2 + BLOCK_SIZE, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+        data = mmap(nullptr, size * 2 + BLOCK_SIZE,
+                PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 
         ASSERT_POSTCONDITION(data,
                 "couldn't allocate %u KiB of virtual address space for the command buffer",