#endif
#ifndef I_MULTIPLICITY
-# if defined(MULTIPLICITY) || defined(PERL_IMPLICIT_CONTEXT)
+# if defined(MULTIPLICITY)
# define I_MULTIPLICITY 1
# else
# define I_MULTIPLICITY 0
# endif
#endif
+#if I_MULTIPLICITY
+# ifndef PERL_IMPLICIT_CONTEXT
+# error MULTIPLICITY builds must set PERL_IMPLICIT_CONTEXT
+# endif
+#endif
#if I_MULTIPLICITY && !defined(tTHX)
# define tTHX PerlInterpreter*
#endif