diff --git a/src/symbolize/libbacktrace.rs b/src/symbolize/libbacktrace.rs
index 23706da02..5fd6476e8 100644
--- a/src/symbolize/libbacktrace.rs
+++ b/src/symbolize/libbacktrace.rs
@@ -124,7 +124,7 @@ unsafe fn call(data: *mut c_void, sym: &Symbol) {
 // that is calculated the first time this is requested. Remember that
 // backtracing all happens serially (one global lock).
 //
-// An additionally oddity in this function is that we initialize the
+// An additional oddity in this function is that we initialize the
 // filename via self_exe_name() to pass to libbacktrace. It turns out
 // that on Linux libbacktrace seamlessly gets the filename of the
 // current executable, but this fails on freebsd. by always providing
@@ -159,6 +159,8 @@ unsafe fn init_state() -> *mut bt::backtrace_state {
             }
             None => ptr::null(),
         };
+        // Our libbacktrace may not have multithreading support, so
+        // set `threaded = 0` and synchronize ourselves.
         STATE = bt::backtrace_create_state(filename, 0, error_cb,
                                            ptr::null_mut());
     });
@@ -184,6 +186,7 @@ pub fn resolve(symaddr: *mut c_void, mut cb: &mut FnMut(&Symbol)) {
         if state.is_null() {
             return
         }
+        let _guard = ::lock::lock();
 
         let ret = bt::backtrace_pcinfo(state, symaddr as uintptr_t,
                                        pcinfo_cb, error_cb,