diff --git a/Modules/regexpr.h b/Modules/regexpr.h
index 8c5a2ac..c0276ae 100644
--- a/Modules/regexpr.h
+++ b/Modules/regexpr.h
@@ -19,6 +19,11 @@
 #ifndef REGEXPR_H
 #define REGEXPR_H
 
+#if defined(__STDC__) || defined(THINK_C)
+#undef HAVE_PROTOTYPES
+#define HAVE_PROTOTYPES
+#endif
+
 #define RE_NREGS	10  /* number of registers available */
 
 typedef struct re_pattern_buffer
@@ -56,7 +61,7 @@
 #define RE_SYNTAX_GREP	(RE_BK_PLUS_QM|RE_NEWLINE_OR)
 #define RE_SYNTAX_EMACS	0
 
-#ifdef __STDC__
+#ifdef HAVE_PROTOTYPES
 
 int re_set_syntax(int syntax);
 /* This sets the syntax to use and returns the previous syntax.  The
@@ -116,7 +121,7 @@
    matches the regular expression (that is, a matching part is found
    anywhere in the string). */
 
-#else /* __STDC__ */
+#else /* HAVE_PROTOTYPES */
 
 int re_set_syntax();
 char *re_compile_pattern();
@@ -128,7 +133,7 @@
 char *re_comp();
 int re_exec();
 
-#endif /* __STDC__ */
+#endif /* HAVE_PROTOTYPES */
 
 #endif /* REGEXPR_H */