diff --git a/src/chars.c b/src/chars.c
index 449ec2da8751b66b1419e9ce2521ecc698129328..b09ba9e1837817ad9e13e54fc9aac261a0a20daa 100644
--- a/src/chars.c
+++ b/src/chars.c
@@ -47,7 +47,7 @@ int nisblank(int c)
 }
 #endif
 
-#if defined(NANO_WIDE) && !defined(HAVE_ISWBLANK)
+#if !defined(HAVE_ISWBLANK) && defined(NANO_WIDE)
 /* This function is equivalent to iswblank(). */
 int niswblank(wchar_t wc)
 {
diff --git a/src/proto.h b/src/proto.h
index dc408f4102521d6af0b2dc74dcf742d7da529571..d6462223572056b31b8b6fc7d9a0860262967558 100644
--- a/src/proto.h
+++ b/src/proto.h
@@ -162,7 +162,7 @@ extern char *homedir;
 #ifndef HAVE_ISBLANK
 int nisblank(int c);
 #endif
-#if defined(NANO_WIDE) && !defined(HAVE_ISWBLANK)
+#if !defined(HAVE_ISWBLANK) && defined(NANO_WIDE)
 int niswblank(wchar_t wc);
 #endif
 bool is_byte(int c);