diff --git a/include/linux/signal.h b/include/linux/signal.h
index 750196f..ab1e039 100644
--- a/include/linux/signal.h
+++ b/include/linux/signal.h
@@ -2,6 +2,7 @@
 #define _LINUX_SIGNAL_H
 
 #include <linux/list.h>
+#include <linux/bug.h>
 #include <uapi/linux/signal.h>
 
 struct task_struct;
@@ -67,7 +68,6 @@
 
 static inline int sigisemptyset(sigset_t *set)
 {
-	extern void _NSIG_WORDS_is_unsupported_size(void);
 	switch (_NSIG_WORDS) {
 	case 4:
 		return (set->sig[3] | set->sig[2] |
@@ -77,7 +77,7 @@
 	case 1:
 		return set->sig[0] == 0;
 	default:
-		_NSIG_WORDS_is_unsupported_size();
+		BUILD_BUG();
 		return 0;
 	}
 }
@@ -90,24 +90,23 @@
 #define _SIG_SET_BINOP(name, op)					\
 static inline void name(sigset_t *r, const sigset_t *a, const sigset_t *b) \
 {									\
-	extern void _NSIG_WORDS_is_unsupported_size(void);		\
 	unsigned long a0, a1, a2, a3, b0, b1, b2, b3;			\
 									\
 	switch (_NSIG_WORDS) {						\
-	    case 4:							\
+	case 4:								\
 		a3 = a->sig[3]; a2 = a->sig[2];				\
 		b3 = b->sig[3]; b2 = b->sig[2];				\
 		r->sig[3] = op(a3, b3);					\
 		r->sig[2] = op(a2, b2);					\
-	    case 2:							\
+	case 2:								\
 		a1 = a->sig[1]; b1 = b->sig[1];				\
 		r->sig[1] = op(a1, b1);					\
-	    case 1:							\
+	case 1:								\
 		a0 = a->sig[0]; b0 = b->sig[0];				\
 		r->sig[0] = op(a0, b0);					\
 		break;							\
-	    default:							\
-		_NSIG_WORDS_is_unsupported_size();			\
+	default:							\
+		BUILD_BUG();						\
 	}								\
 }
 
@@ -128,16 +127,14 @@
 #define _SIG_SET_OP(name, op)						\
 static inline void name(sigset_t *set)					\
 {									\
-	extern void _NSIG_WORDS_is_unsupported_size(void);		\
-									\
 	switch (_NSIG_WORDS) {						\
-	    case 4: set->sig[3] = op(set->sig[3]);			\
-		    set->sig[2] = op(set->sig[2]);			\
-	    case 2: set->sig[1] = op(set->sig[1]);			\
-	    case 1: set->sig[0] = op(set->sig[0]);			\
+	case 4:	set->sig[3] = op(set->sig[3]);				\
+		set->sig[2] = op(set->sig[2]);				\
+	case 2:	set->sig[1] = op(set->sig[1]);				\
+	case 1:	set->sig[0] = op(set->sig[0]);				\
 		    break;						\
-	    default:							\
-		_NSIG_WORDS_is_unsupported_size();			\
+	default:							\
+		BUILD_BUG();						\
 	}								\
 }