diff --git a/libguile/gc_os_dep.c b/libguile/gc_os_dep.c
index d89f1cf10..7bc96447f 100644
--- a/libguile/gc_os_dep.c
+++ b/libguile/gc_os_dep.c
@@ -1127,7 +1127,7 @@ scm_get_stack_base ()
 #   ifdef OSF1
 #	define OS_TYPE "OSF1"
 #   	define DATASTART ((ptr_t) 0x140000000)
-	extern _end;
+	extern int _end;
 #   	define DATAEND ((ptr_t) &_end)
 #   	define HEURISTIC2
 	/* Normally HEURISTIC2 is too conervative, since		*/
@@ -1912,7 +1912,7 @@ void *scm_get_stack_base()
 #	    if STACK_GROWS_DOWN
 		result = GC_find_limit((ptr_t)(&dummy), TRUE);
 #           	ifdef HEURISTIC2_LIMIT
-		    if (result > HEURISTIC2_LIMIT
+		    if ((ptr_t)result > HEURISTIC2_LIMIT
 		        && (ptr_t)(&dummy) < HEURISTIC2_LIMIT) {
 		            result = HEURISTIC2_LIMIT;
 		    }