diff --git a/src/lisp/backtrace.c b/src/lisp/backtrace.c
index 871b692f5f72b98c7bfd846ef307c9d38f250e77..5e6ff9a6351523d3e55e5cf160713e9fd65f6317 100644
--- a/src/lisp/backtrace.c
+++ b/src/lisp/backtrace.c
@@ -252,7 +252,7 @@ backtrace(int nframes)
 static int
 stack_pointer_p(unsigned long p)
 {
-    return (p < CONTROL_STACK_START + control_stack_size
+    return ((void *)p < (void *)control_stack + control_stack_size
 	    && p > (unsigned long) &p && (p & 3) == 0);
 }