diff --git a/libbacktrace/UnwindPtrace.cpp b/libbacktrace/UnwindPtrace.cpp
index 7a9bbdd..6fecb76 100644
--- a/libbacktrace/UnwindPtrace.cpp
+++ b/libbacktrace/UnwindPtrace.cpp
@@ -82,6 +82,7 @@
     if (num_ignore_frames == 0) {
       size_t num_frames = backtrace->num_frames;
       backtrace_frame_data_t* frame = &backtrace->frames[num_frames];
+      frame->num = num_frames;
       frame->pc = static_cast<uintptr_t>(pc);
       frame->sp = static_cast<uintptr_t>(sp);
       frame->stack_size = 0;