diff --git a/usr.bin/lex/flex.skl b/usr.bin/lex/flex.skl
index 460b2fa575ef..21117118fd62 100644
--- a/usr.bin/lex/flex.skl
+++ b/usr.bin/lex/flex.skl
@@ -747,7 +747,7 @@ void yyFlexLexer::LexerOutput( const char* buf, int size )
  */
 
 %-
-static int yy_get_next_buffer()
+static int yy_get_next_buffer(void)
 %+
 int yyFlexLexer::yy_get_next_buffer()
 %*
@@ -883,7 +883,7 @@ int yyFlexLexer::yy_get_next_buffer()
 /* yy_get_previous_state - get the state just before the EOB char was reached */
 
 %-
-static yy_state_type yy_get_previous_state()
+static yy_state_type yy_get_previous_state(void)
 %+
 yy_state_type yyFlexLexer::yy_get_previous_state()
 %*
@@ -982,7 +982,7 @@ void yyFlexLexer::yyunput( int c, char* yy_bp )
 #ifdef __cplusplus
 static int yyinput()
 #else
-static int input()
+static int input(void)
 #endif
 %+
 int yyFlexLexer::yyinput()
diff --git a/usr.bin/lex/initscan.c b/usr.bin/lex/initscan.c
index 7617c693dd40..59c81f7512fa 100644
--- a/usr.bin/lex/initscan.c
+++ b/usr.bin/lex/initscan.c
@@ -2894,7 +2894,7 @@ case YY_STATE_EOF(LINEDIR):
  *	EOB_ACT_END_OF_FILE - end of file
  */
 
-static int yy_get_next_buffer()
+static int yy_get_next_buffer(void)
 	{
 	char *dest = yy_current_buffer->yy_ch_buf;
 	char *source = yytext_ptr;
@@ -3026,7 +3026,7 @@ static int yy_get_next_buffer()
 
 /* yy_get_previous_state - get the state just before the EOB char was reached */
 
-static yy_state_type yy_get_previous_state()
+static yy_state_type yy_get_previous_state(void)
 	{
 	yy_state_type yy_current_state;
 	char *yy_cp;
@@ -3138,7 +3138,7 @@ char *yy_bp;
 #ifdef __cplusplus
 static int yyinput()
 #else
-static int input()
+static int input(void)
 #endif
 	{
 	int c;
diff --git a/usr.bin/yacc/skeleton.c b/usr.bin/yacc/skeleton.c
index 8ff7c8a122f1..434a7c231dbf 100644
--- a/usr.bin/yacc/skeleton.c
+++ b/usr.bin/yacc/skeleton.c
@@ -140,7 +140,11 @@ const char *header[] =
 const char *body[] =
 {
     "/* allocate initial stack or double stack size, up to YYMAXDEPTH */",
+    "#if defined(__cplusplus) || __STDC__",
+    "static int yygrowstack(void)",
+    "#else",
     "static int yygrowstack()",
+    "#endif",
     "{",
     "    int newsize, i;",
     "    short *newss;",