diff --git a/src/vim.h b/src/vim.h
index 8d0f3e0..6533a45 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -242,6 +242,9 @@
 #if (defined(UNIX) || defined(VMS)) \
 	&& (!defined(MACOS_X) || defined(HAVE_CONFIG_H))
 # include "os_unix.h"	    // bring lots of system header files
+#else
+  // For all non-Unix systems: use old-fashioned signal().
+# define mch_signal(signum, sighandler) signal(signum, sighandler)
 #endif
 
 // Mark unused function arguments with UNUSED, so that gcc -Wunused-parameter