Index: lib/sanitizer_common/sanitizer_stacktrace_libcdep.cc
===================================================================
--- lib/sanitizer_common/sanitizer_stacktrace_libcdep.cc
+++ lib/sanitizer_common/sanitizer_stacktrace_libcdep.cc
@@ -60,10 +60,14 @@
     return;
   }
   if (!WillUseFastUnwind(request_fast_unwind)) {
+#if SANITIZER_CAN_SLOW_UNWIND
     if (context)
       SlowUnwindStackWithContext(pc, context, max_depth);
     else
       SlowUnwindStack(pc, max_depth);
+#else
+    UNREACHABLE("slow unwind requested but not available");
+#endif
   } else {
     FastUnwindStack(pc, bp, stack_top, stack_bottom, max_depth);
   }