It seems the iOS Asan runtime has a false positive around aligned_alloc. Steps to reproduce: Create a new empty ObjC iOS project, then at the beginning insert the line: free(aligned_alloc(16, 128)); Check the "Address Sanitizer" box in the Scheme->Run->Diagnostics, then run it on a device. Result: There is a workaround, however, for anyone else who runs into this--insert this snippet somewhere in your project in global scope. It seems like posix_memalign does not have the same issue. #if defined(__has_feature) && __has_feature(address_sanitizer) extern "C" void *aligned_alloc(size_t __alignment, size_t __size) { void* ret; int res = ::posix_memalign(&ret, __alignment, __size); if (res == 0) { return ret; } return nullptr; } #endif