diff --git a/libbacktrace/ChangeLog b/libbacktrace/ChangeLog
index 60ae5d2788d..c88b1238bb6 100644
--- a/libbacktrace/ChangeLog
+++ b/libbacktrace/ChangeLog
@@ -1,3 +1,10 @@
+2019-09-26  Ian Lance Taylor  <iant@golang.org>
+
+	PR libbacktrace/91908
+	* pecoff.c (backtrace_initialize): Explicitly cast unchecked
+	__sync_bool_compare_and_swap to void.
+	* xcoff.c (backtrace_initialize): Likewise.
+
 2019-09-03  Ulrich Weigand  <uweigand@de.ibm.com>
 
 	* configure.ac: Remove references to spu.
diff --git a/libbacktrace/pecoff.c b/libbacktrace/pecoff.c
index da1982fd3ca..fcf9508d488 100644
--- a/libbacktrace/pecoff.c
+++ b/libbacktrace/pecoff.c
@@ -922,7 +922,8 @@ backtrace_initialize (struct backtrace_state *state,
       if (found_sym)
 	backtrace_atomic_store_pointer (&state->syminfo_fn, coff_syminfo);
       else
-	__sync_bool_compare_and_swap (&state->syminfo_fn, NULL, coff_nosyms);
+	(void) __sync_bool_compare_and_swap (&state->syminfo_fn, NULL,
+					     coff_nosyms);
     }
 
   if (!state->threaded)
diff --git a/libbacktrace/xcoff.c b/libbacktrace/xcoff.c
index d50b5bc517e..bc60962fe04 100644
--- a/libbacktrace/xcoff.c
+++ b/libbacktrace/xcoff.c
@@ -1592,7 +1592,8 @@ backtrace_initialize (struct backtrace_state *state,
       if (found_sym)
 	backtrace_atomic_store_pointer (&state->syminfo_fn, xcoff_syminfo);
       else
-	__sync_bool_compare_and_swap (&state->syminfo_fn, NULL, xcoff_nosyms);
+	(void) __sync_bool_compare_and_swap (&state->syminfo_fn, NULL,
+					     xcoff_nosyms);
     }
 
   if (!state->threaded)