diff --git a/src/gc-alloc-profiler.cpp b/src/gc-alloc-profiler.cpp
index 4846d7f7f7fb1..6d0af5cb9c1b6 100644
--- a/src/gc-alloc-profiler.cpp
+++ b/src/gc-alloc-profiler.cpp
@@ -54,9 +54,11 @@ jl_raw_backtrace_t get_raw_backtrace() JL_NOTSAFEPOINT {
     // per-thread backtrace buffer.
     jl_ptls_t ptls = jl_current_task->ptls;
     jl_bt_element_t *shared_bt_data_buffer = ptls->profiling_bt_buffer;
-    if (shared_bt_data_buffer == NULL)
-        ptls->profiling_bt_buffer = shared_bt_data_buffer = \
-                malloc_s(sizeof(jl_bt_element_t) * (JL_MAX_BT_SIZE + 1));
+    if (shared_bt_data_buffer == NULL) {
+        size_t size = sizeof(jl_bt_element_t) * (JL_MAX_BT_SIZE + 1);
+        shared_bt_data_buffer = (jl_bt_element_t*) malloc_s(size);
+        ptls->profiling_bt_buffer = shared_bt_data_buffer;
+    }
 
     size_t bt_size = rec_backtrace(shared_bt_data_buffer, JL_MAX_BT_SIZE, 2);