--- misc/liblangtag-0.4.0/liblangtag/lt-macros.h
+++ misc/build/liblangtag-0.4.0/liblangtag/lt-macros.h
@@ -203,6 +203,7 @@
 	LT_STMT_START {__asm__ __volatile__ ("bpt");} LT_STMT_END
 #else
+#  include <signal.h>
 #  define LT_BREAKPOINT()				\
 	LT_STMT_START {raise(SIGTRAP);} LT_STMT_END
 #endif