diff --git a/src/RE.h b/src/RE.h
index 4a9c0ee6bb..5ba41531f8 100644
--- a/src/RE.h
+++ b/src/RE.h
@@ -15,7 +15,7 @@
 using cce_func = int (*)(int);
 
 // This method is automatically generated by flex and shouldn't be namespaced
-extern int re_lex(void);
+extern int re_lex();
 
 namespace zeek {
 
diff --git a/src/RuleMatcher.h b/src/RuleMatcher.h
index fba28212b2..bf8d8b8d1e 100644
--- a/src/RuleMatcher.h
+++ b/src/RuleMatcher.h
@@ -23,9 +23,9 @@
 extern void rules_error(const char* msg);
 extern void rules_error(const char* msg, const char* addl);
 extern void rules_error(zeek::detail::Rule* id, const char* msg);
-extern int rules_lex(void);
-extern int rules_parse(void);
-extern "C" int rules_wrap(void);
+extern int rules_lex();
+extern int rules_parse();
+extern "C" int rules_wrap();
 extern int rules_line_number;
 extern const char* current_rule_file;