diff --git a/slirp/ip_icmp.h b/slirp/ip_icmp.h
index 03301313e0..e793990d28 100644
--- a/slirp/ip_icmp.h
+++ b/slirp/ip_icmp.h
@@ -153,9 +153,9 @@ struct icmp {
 	(type) == ICMP_IREQ || (type) == ICMP_IREQREPLY || \
 	(type) == ICMP_MASKREQ || (type) == ICMP_MASKREPLY)
 
-void icmp_input _P((struct mbuf *, int));
+void icmp_input(struct mbuf *, int);
 void icmp_error(struct mbuf *msrc, u_char type, u_char code, int minsize,
                 const char *message);
-void icmp_reflect _P((struct mbuf *));
+void icmp_reflect(struct mbuf *);
 
 #endif
diff --git a/slirp/mbuf.h b/slirp/mbuf.h
index 99fca43898..97729e24b0 100644
--- a/slirp/mbuf.h
+++ b/slirp/mbuf.h
@@ -115,13 +115,13 @@ struct mbuf {
 #define M_DOFREE		0x08	/* when m_free is called on the mbuf, free()
 					 * it rather than putting it on the free list */
 
-void m_init _P((Slirp *));
-struct mbuf * m_get _P((Slirp *));
-void m_free _P((struct mbuf *));
-void m_cat _P((register struct mbuf *, register struct mbuf *));
-void m_inc _P((struct mbuf *, int));
-void m_adj _P((struct mbuf *, int));
-int m_copy _P((struct mbuf *, struct mbuf *, int, int));
-struct mbuf * dtom _P((Slirp *, void *));
+void m_init(Slirp *);
+struct mbuf * m_get(Slirp *);
+void m_free(struct mbuf *);
+void m_cat(register struct mbuf *, register struct mbuf *);
+void m_inc(struct mbuf *, int);
+void m_adj(struct mbuf *, int);
+int m_copy(struct mbuf *, struct mbuf *, int, int);
+struct mbuf * dtom(Slirp *, void *);
 
 #endif
diff --git a/slirp/misc.h b/slirp/misc.h
index e43519dcba..c335394356 100644
--- a/slirp/misc.h
+++ b/slirp/misc.h
@@ -17,10 +17,10 @@ struct ex_list {
 };
 
 #ifndef HAVE_STRDUP
-char *strdup _P((const char *));
+char *strdup(const char *);
 #endif
 
-void do_wait _P((int));
+void do_wait(int);
 
 #define EMU_NONE 0x0
 
@@ -58,20 +58,20 @@ struct emu_t {
 
 extern int x_port, x_server, x_display;
 
-int show_x _P((char *, struct socket *));
-void redir_x _P((u_int32_t, int, int, int));
-void slirp_insque _P((void *, void *));
-void slirp_remque _P((void *));
-int add_exec _P((struct ex_list **, int, char *, struct in_addr, int));
-int slirp_openpty _P((int *, int *));
+int show_x(char *, struct socket *);
+void redir_x(u_int32_t, int, int, int);
+void slirp_insque(void *, void *);
+void slirp_remque(void *);
+int add_exec(struct ex_list **, int, char *, struct in_addr, int);
+int slirp_openpty(int *, int *);
 int fork_exec(struct socket *so, const char *ex, int do_pty);
-void snooze_hup _P((int));
-void snooze _P((void));
-void relay _P((int));
-void add_emu _P((char *));
-void u_sleep _P((int));
-void fd_nonblock _P((int));
-void fd_block _P((int));
-int rsh_exec _P((struct socket *, struct socket *, char *, char *, char *));
+void snooze_hup(int);
+void snooze(void);
+void relay(int);
+void add_emu(char *);
+void u_sleep(int);
+void fd_nonblock(int);
+void fd_block(int);
+int rsh_exec(struct socket *, struct socket *, char *, char *, char *);
 
 #endif
diff --git a/slirp/sbuf.h b/slirp/sbuf.h
index a4f103623a..4f22e7c388 100644
--- a/slirp/sbuf.h
+++ b/slirp/sbuf.h
@@ -21,10 +21,10 @@ struct sbuf {
 	char	*sb_data;	/* Actual data */
 };
 
-void sbfree _P((struct sbuf *));
-void sbdrop _P((struct sbuf *, int));
-void sbreserve _P((struct sbuf *, int));
-void sbappend _P((struct socket *, struct mbuf *));
-void sbcopy _P((struct sbuf *, int, int, char *));
+void sbfree(struct sbuf *);
+void sbdrop(struct sbuf *, int);
+void sbreserve(struct sbuf *, int);
+void sbappend(struct socket *, struct mbuf *);
+void sbcopy(struct sbuf *, int, int, char *);
 
 #endif
diff --git a/slirp/slirp.h b/slirp/slirp.h
index 920d7a6213..22058cd05e 100644
--- a/slirp/slirp.h
+++ b/slirp/slirp.h
@@ -103,13 +103,6 @@ typedef unsigned char u_int8_t;
 #include <sys/uio.h>
 #endif
 
-#undef _P
-#ifndef NO_PROTOTYPES
-#  define   _P(x)   x
-#else
-#  define   _P(x)   ()
-#endif
-
 #ifndef _WIN32
 #include <netinet/in.h>
 #include <arpa/inet.h>
@@ -121,17 +114,17 @@ typedef unsigned char u_int8_t;
 
 /* Systems lacking strdup() definition in <string.h>. */
 #if defined(ultrix)
-char *strdup _P((const char *));
+char *strdup(const char *);
 #endif
 
 /* Systems lacking malloc() definition in <stdlib.h>. */
 #if defined(ultrix) || defined(hcx)
-void *malloc _P((size_t arg));
-void free _P((void *ptr));
+void *malloc(size_t arg);
+void free(void *ptr);
 #endif
 
 #ifndef HAVE_INET_ATON
-int inet_aton _P((const char *cp, struct in_addr *ia));
+int inet_aton(const char *cp, struct in_addr *ia);
 #endif
 
 #include <fcntl.h>
@@ -270,38 +263,38 @@ extern Slirp *slirp_instance;
 #endif
 
 #ifndef FULL_BOLT
-void if_start _P((Slirp *));
+void if_start(Slirp *);
 #else
-void if_start _P((struct ttys *));
+void if_start(struct ttys *);
 #endif
 
 #ifdef BAD_SPRINTF
 # define vsprintf vsprintf_len
 # define sprintf sprintf_len
- extern int vsprintf_len _P((char *, const char *, va_list));
- extern int sprintf_len _P((char *, const char *, ...));
+ extern int vsprintf_len(char *, const char *, va_list);
+ extern int sprintf_len(char *, const char *, ...);
 #endif
 
 #ifdef DECLARE_SPRINTF
 # ifndef BAD_SPRINTF
- extern int vsprintf _P((char *, const char *, va_list));
+ extern int vsprintf(char *, const char *, va_list);
 # endif
- extern int vfprintf _P((FILE *, const char *, va_list));
+ extern int vfprintf(FILE *, const char *, va_list);
 #endif
 
 #ifndef HAVE_STRERROR
- extern char *strerror _P((int error));
+ extern char *strerror(int error);
 #endif
 
 #ifndef HAVE_INDEX
- char *index _P((const char *, int));
+ char *index(const char *, int);
 #endif
 
 #ifndef HAVE_GETHOSTID
- long gethostid _P((void));
+ long gethostid(void);
 #endif
 
-void lprint _P((const char *, ...));
+void lprint(const char *, ...);
 
 #ifndef _WIN32
 #include <netdb.h>
@@ -316,39 +309,39 @@ void lprint _P((const char *, ...));
 int cksum(struct mbuf *m, int len);
 
 /* if.c */
-void if_init _P((Slirp *));
-void if_output _P((struct socket *, struct mbuf *));
+void if_init(Slirp *);
+void if_output(struct socket *, struct mbuf *);
 
 /* ip_input.c */
-void ip_init _P((Slirp *));
-void ip_input _P((struct mbuf *));
-void ip_slowtimo _P((Slirp *));
-void ip_stripoptions _P((register struct mbuf *, struct mbuf *));
+void ip_init(Slirp *);
+void ip_input(struct mbuf *);
+void ip_slowtimo(Slirp *);
+void ip_stripoptions(register struct mbuf *, struct mbuf *);
 
 /* ip_output.c */
-int ip_output _P((struct socket *, struct mbuf *));
+int ip_output(struct socket *, struct mbuf *);
 
 /* tcp_input.c */
-void tcp_input _P((register struct mbuf *, int, struct socket *));
-int tcp_mss _P((register struct tcpcb *, u_int));
+void tcp_input(register struct mbuf *, int, struct socket *);
+int tcp_mss(register struct tcpcb *, u_int);
 
 /* tcp_output.c */
-int tcp_output _P((register struct tcpcb *));
-void tcp_setpersist _P((register struct tcpcb *));
+int tcp_output(register struct tcpcb *);
+void tcp_setpersist(register struct tcpcb *);
 
 /* tcp_subr.c */
-void tcp_init _P((Slirp *));
-void tcp_template _P((struct tcpcb *));
-void tcp_respond _P((struct tcpcb *, register struct tcpiphdr *, register struct mbuf *, tcp_seq, tcp_seq, int));
-struct tcpcb * tcp_newtcpcb _P((struct socket *));
-struct tcpcb * tcp_close _P((register struct tcpcb *));
-void tcp_sockclosed _P((struct tcpcb *));
-int tcp_fconnect _P((struct socket *));
-void tcp_connect _P((struct socket *));
-int tcp_attach _P((struct socket *));
-u_int8_t tcp_tos _P((struct socket *));
-int tcp_emu _P((struct socket *, struct mbuf *));
-int tcp_ctl _P((struct socket *));
+void tcp_init(Slirp *);
+void tcp_template(struct tcpcb *);
+void tcp_respond(struct tcpcb *, register struct tcpiphdr *, register struct mbuf *, tcp_seq, tcp_seq, int);
+struct tcpcb * tcp_newtcpcb(struct socket *);
+struct tcpcb * tcp_close(register struct tcpcb *);
+void tcp_sockclosed(struct tcpcb *);
+int tcp_fconnect(struct socket *);
+void tcp_connect(struct socket *);
+int tcp_attach(struct socket *);
+u_int8_t tcp_tos(struct socket *);
+int tcp_emu(struct socket *, struct mbuf *);
+int tcp_ctl(struct socket *);
 struct tcpcb *tcp_drop(struct tcpcb *tp, int err);
 
 #ifdef USE_PPP
diff --git a/slirp/socket.h b/slirp/socket.h
index dcf27430b2..6e85d03588 100644
--- a/slirp/socket.h
+++ b/slirp/socket.h
@@ -74,20 +74,20 @@ struct socket {
 #define SS_HOSTFWD		0x1000	/* Socket describes host->guest forwarding */
 #define SS_INCOMING		0x2000	/* Connection was initiated by a host on the internet */
 
-struct socket * solookup _P((struct socket *, struct in_addr, u_int, struct in_addr, u_int));
-struct socket * socreate _P((Slirp *));
-void sofree _P((struct socket *));
-int soread _P((struct socket *));
-void sorecvoob _P((struct socket *));
-int sosendoob _P((struct socket *));
-int sowrite _P((struct socket *));
-void sorecvfrom _P((struct socket *));
-int sosendto _P((struct socket *, struct mbuf *));
-struct socket * tcp_listen _P((Slirp *, u_int32_t, u_int, u_int32_t, u_int,
-                               int));
-void soisfconnecting _P((register struct socket *));
-void soisfconnected _P((register struct socket *));
-void sofwdrain _P((struct socket *));
+struct socket * solookup(struct socket *, struct in_addr, u_int, struct in_addr, u_int);
+struct socket * socreate(Slirp *);
+void sofree(struct socket *);
+int soread(struct socket *);
+void sorecvoob(struct socket *);
+int sosendoob(struct socket *);
+int sowrite(struct socket *);
+void sorecvfrom(struct socket *);
+int sosendto(struct socket *, struct mbuf *);
+struct socket * tcp_listen(Slirp *, u_int32_t, u_int, u_int32_t, u_int,
+                               int);
+void soisfconnecting(register struct socket *);
+void soisfconnected(register struct socket *);
+void sofwdrain(struct socket *);
 struct iovec; /* For win32 */
 size_t sopreprbuf(struct socket *so, struct iovec *iov, int *np);
 int soreadbuf(struct socket *so, const char *buf, int size);
diff --git a/slirp/tcp_timer.h b/slirp/tcp_timer.h
index cfb06ffc87..ff17914f41 100644
--- a/slirp/tcp_timer.h
+++ b/slirp/tcp_timer.h
@@ -120,8 +120,8 @@ extern const int tcp_backoff[];
 
 struct tcpcb;
 
-void tcp_fasttimo _P((Slirp *));
-void tcp_slowtimo _P((Slirp *));
-void tcp_canceltimers _P((struct tcpcb *));
+void tcp_fasttimo(Slirp *);
+void tcp_slowtimo(Slirp *);
+void tcp_canceltimers(struct tcpcb *);
 
 #endif
diff --git a/slirp/udp.h b/slirp/udp.h
index cc814a3f48..47d2f3d4cd 100644
--- a/slirp/udp.h
+++ b/slirp/udp.h
@@ -73,13 +73,13 @@ struct udpiphdr {
 
 struct mbuf;
 
-void udp_init _P((Slirp *));
-void udp_input _P((register struct mbuf *, int));
-int udp_output _P((struct socket *, struct mbuf *, struct sockaddr_in *));
-int udp_attach _P((struct socket *));
-void udp_detach _P((struct socket *));
-struct socket * udp_listen _P((Slirp *, u_int32_t, u_int, u_int32_t, u_int,
-                               int));
+void udp_init(Slirp *);
+void udp_input(register struct mbuf *, int);
+int udp_output(struct socket *, struct mbuf *, struct sockaddr_in *);
+int udp_attach(struct socket *);
+void udp_detach(struct socket *);
+struct socket * udp_listen(Slirp *, u_int32_t, u_int, u_int32_t, u_int,
+                           int);
 int udp_output2(struct socket *so, struct mbuf *m,
                 struct sockaddr_in *saddr, struct sockaddr_in *daddr,
                 int iptos);